That reminds me: don't forget to apply encumbrance penalties to the mount's skill checks. Any horse carrying a rider will probably be at Medium encumbrance, which gives a -3 penalty to all skills where ACP applies. A smaller horse could even end up at Heavy encumbrance, for a -6 penalty.ajanders said:Balance checks might be relevant here...
For an animal with only a +1 Balance modifier to begin with, that's reason enough to dismount when crossing unsafe ground.