[QuickSilver]

Hi there! My guess is that he'll grow out of it, but here is a training suggestion:

Try to make him associate the leather with something unpleasant. He can probably tell which pieces have bitter apple on them and which don't, and when you use the leave it command, he is obeying you rather than avoiding the leather per se.

I would try some training sessions *just* to avoid leather. Try putting him on the floor with a bunch of leather pieces, while you and your husband sit on opposite ends of the room, each with a can of pennies. When he checks out the leather, one of you shakes your can. You can also try throwing him scraps of leather, and then shaking the can. The point is to actually scare him a bit and convince him that leather is bad in and of itself.

I'm not sure this will work with the scrap size you're talking about, but another trick is to put a piece of leather on the edge of a coffee table, tied to a loaded can with a piece of thread. When he grabs the leather, the can falls and scares him. This has the benefit of making a scary noise "on its own", hopefully convincing him to avoid leather altogether, not just when you are around.

Normally I wouldn't suggest aversive training, but I assume eating leather could be really bad for him, and worth making him a little scared of it.