Neonchameleon
Legend
An attempt by players to go "OA fishing", same as with "Critical fishing" or "Save or Die fishing" or any number of such "Push it until it breaks fishing" things--is a sign that something is out of whack with the mechanic.
Out of curiosity, who goes "OA fishing"? The nearest I've seen are provoke-tactics which are the equivalent of a gambit in chess. You want to be OA'd because you think it's bad for the monster. But that (a) is relying on the Defender's punishment and (b) is something the monster has complete control over. I don't see the ability to offer gambits that the monster need not accept to be a problem.
Now AoO fishing is another story. Just ask all the spiky-chain-death-trippers of doom. The something out of whack there with the mechanics is that standing up from prone provokes an AoO. So tripping someone effectively forces them to either provoke AoOs or to fight from down on the floor. Here's where the break is.
Question. Everyone seems very focused on the idea of being able to stop/hinder movement with OAs. Is this important in itself, or is it purely a means to the end of "the fighter can protect the squishy wizard?" From the point of view of the guy making the OA, what do you want that capability for?
Another question. Is it necessary for everyone to be able to make OAs? Or could it perhaps work as a special ability that only certain combatants (e.g., fighters, defendery monsters) have?
First there's the genuine protection aspect. Second there's the "I want to face OAs". I don't want to make dancing a conga line round the enemy too easy - I want it to come with a sense of cool and a sense of achievement. Third there's the issue round flanking. I consider facing in a game using 6 second turns to be generally a mistake for bipeds as you can turn fast. (Unless in a pikeblock or shieldwall). But allow free movement and flanking becomes trivial. You need some sort of protection without completely eliminating flexibility.
It's not just the fighter who needs to be able to hold the battle line - the fighter should simply be very comfortably be best at it. Of course having the wizard as unable to make an AoO wouldn't be a problem. But I'd rather a default as yes here.