You do need to keep him contained whenever you are not there watching him. Whether that means "chaining" him, keeping him in a very secure pen or crating him. Ideally, he should be tethered to you when outside also. Containing him is much better than re-homing him this late in his life, especially since he's a hybrid. He really should NOT be allowed to roam, ever. A roaming dog is in extreme danger. A roaming wolf with very high prey drive who kills cats, and snaps at livestock and children is beyond a liability!

Have you tried keeping the cats inside, in a room to their own when you are not home? You need to keep their safety as a priority, the cats shouldn't be loose while the dog is loose with no supervision. Ideally, a wolf hybrid just shouldn't be around cats at all with that much prey drive.

I've only known 2 hybrids, so other people with more experience probably have much better advice.