Need help selecting English bit... again

So I rode Mellow for the third time today with just a simple loose ring snaffle (my mare's) and I might as well have had nothing in his mouth at all. I'm starting to think that a mild french link snaffle might not work for him. Any suggestions?

Are you sure there is no underlying training problem?

There might be. He's a very stubborn little pony. He was hell bent on getting back to his pasture mate. Refused to turn right. Got off and tried to get him to back up manually, and he planted those hooves and refused to move. I think he knows how to be a good pony, but he's been out to pasture and allowed to get away with too much.

Does the bit fit-him properly? It sounds like it could be too loose if it's not doing anything.

It definitely sounds like a training thing to me. Take him to his pasture and work his little butt off, and only let him rest when he is facing away from them standing a little ways off....You gotta win every battle and be persistant until he gives, then give a BIG reward.