The bit about needing the check to stay in the saddle is buried semi-deep in the ride skill. Plus past 2nd level the average rider [at 1st with a military sadle] automaticly makes the DC5 check [barring houserules]. That can make the need for the check a touch forgetable. [...In my opinion the DC should be damage taken or 1/2 damage taken but that is another kettle of fish.]
3.0 Ride (DEX)
When the character selects this skill, choose the type of mount the character is familiar with. For this purpose, "horses" includes mules, donkeys, and ponies. If the character uses the skill with a different mount (such as riding a giant lizard when the character is used to riding horses), the character's rank is reduced by 2 (but not below 0). If the character uses this skill with a very different mount (such as riding a griffon when the character is used to riding horses), the character's rank is reduced by 5 (but not below 0).
Check: Typical riding actions don't require checks. The character can saddle, mount, ride, and dismount from a mount without a problem. Mounting or dismounting is a move-equivalent action. Some tasks require checks:
Riding Task DC
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Guide with knees 5
Stay in saddle 5
Fight with warhorse 10
Leap 15
Control Mount in Battle 20
Fast mount or dismount 20*
Cover 15
Soft fall 15
*Armor check penalty applies.
Guide with Knees: the character can react instantly to guide the character's mount with the character's knees so that the character can use both hands in combat. Make the check at the start of the character's round. If the character fails, the character can only use one hand this round because the character needs to use the other to control the character's mount.
Stay in Saddle: The character can react instantly to try to avoid falling when the character's mount rears or bolts unexpectedly or when the character takes damage.
Fight with Warhorse: If the character directs a war-trained mount to attack in battle, the character can still make the character's own attack or attacks normally.
Cover: The character can react instantly to drop down and hang alongside the mount, using it as one-half cover. The character can't attack or cast spells while using the character's mount as cover. If the character fails, the character doesn't get the cover benefit.
Soft Fall: The character reacts instantly to try to take no damage when the character falls off a mount, such as when it is killed or when it falls. If the character fails, the character takes 1d6 points of falling damage.
Leap: The character can get a mount to leap obstacles as part of its movement. Use the character's Ride skill modifier or the mount's Jump skill modifier (whichever is lower) to see how far the mount can jump. The DC (15) is what the character needs to roll to stay on the mount when it leaps.
Control Mount in Battle: As a move-equivalent action, the character can attempt to control a light horse, pony, or heavy horse while in combat. If the character fails, the character can do nothing else that round. The character does not need to roll for warhorses or warponies.
Fast Mount or Dismount: The character can mount or dismount as a free action. If the character fails the check, mounting or dismounting is a move-equivalent action. (The character can't attempt a fast mount or dismount unless the character can perform the mount or dismount as a move-equivalent action this round.)
Special: If the character is riding bareback, the character suffers a –5 penalty on Ride checks.
If the character has 5 or more ranks in Handle Animal, the character gets a +2 synergy bonus to Ride checks.
If the character's mount has a military saddle, it gives a +2 circumstance bonus to Ride checks related to staying in the saddle.
3.5 RIDE (DEX)
If you attempt to ride a creature that is ill suited as a mount, you take a –5 penalty on your Ride checks.
Check: Typical riding actions don’t require checks. You can saddle, mount, ride, and dismount from a mount without a problem.
The following tasks do require checks.
Task Ride DC
Guide with knees 5
Stay in saddle 5
Fight with warhorse 10
Cover 15
Soft fall 15
Task Ride DC
Leap 15
Spur mount 15
Control mount in battle 20
Fast mount or dismount 201
1 Armor check penalty applies.
Guide with Knees: You can react instantly to guide your mount with your knees so that you can use both hands in combat. Make your Ride check at the start of your turn. If you fail, you can use only one hand this round because you need to use the other to control your mount.
Stay in Saddle: You can react instantly to try to avoid falling when your mount rears or bolts unexpectedly or when you take damage. This usage does not take an action.
Fight with Warhorse: If you direct your war-trained mount to attack in battle, you can still make your own attack or attacks normally. This usage is a free action.
Cover: You can react instantly to drop down and hang alongside your mount, using it as cover. You can’t attack or cast spells while using your mount as cover. If you fail your Ride check, you don’t get the cover benefit. This usage does not take an action.
Soft Fall: You can react instantly to try to take no damage when you fall off a mount—when it is killed or when it falls, for example. If you fail your Ride check, you take 1d6 points of falling damage. This usage does not take an action.
Leap: You can get your mount to leap obstacles as part of its movement. Use your Ride modifier or the mount’s Jump modifier, whichever is lower, to see how far the creature can jump. If you fail your Ride check, you fall off the mount when it leaps and take the appropriate falling damage (at least 1d6 points). This usage does not take an action, but is part of the mount’s movement.
Spur Mount: You can spur your mount to greater speed with a move action. A successful Ride check increases the mount’s speed by 10 feet for 1 round but deals 1 point of damage to the creature. You can use this ability every round, but each consecutive round of additional speed deals twice as much damage to the mount as the previous round (2 points, 4 points, 8 points, and so on).
Control Mount in Battle: As a move action, you can attempt to control a light horse, pony, heavy horse, or other mount not trained for combat riding while in battle. If you fail the Ride check, you can do nothing else in that round. You do not need to roll for warhorses or warponies.
Fast Mount or Dismount: You can attempt to mount or dismount from a mount of up to one size category larger than yourself as a free action, provided that you still have a move action available that round. If you fail the Ride check, mounting or dismounting is a move action. You can’t use fast mount or dismount on a mount more than one size category larger than yourself.
Action: Varies. Mounting or dismounting normally is a move action. Other checks are a move action, a free action, or no action at all, as noted above.
Special: If you are riding bareback, you take a –5 penalty on Ride checks.
If your mount has a military saddle you get a +2 circumstance bonus on Ride checks related to staying in the saddle.
The Ride skill is a prerequisite for the feats Mounted Archery, Mounted Combat, Ride-By Attack, Spirited Charge,
Trample.
If you have the Animal Affinity feat, you get a +2 bonus on Ride checks.
Synergy: If you have 5 or more ranks in Handle Animal, you get a +2 bonus on Ride checks.
