Usually when they obsess over it it's rotting and they'll eat it until it's back to good tissue.

You're best bet is skipping the topical application for the most part so he'll get his mind off it. You could try Granulex, it is sweet smelling, I have some that think it's dessert lol But it eats necrotic tissue which sounds like what you may have going on.

Get him away from anything he can hit that tail on and hydrate, hydrate, hydrate.

You could also soak his tail in a bucket of warm water/Epsom salt to promote healing.

Don't give up, you'll get it whipped eventually!

S_B