need collar ideas please

Bella my rescue border collie has so far had 3 collars all of which my bull terrier can take off her neck in seconds, the first one was like a belt buckle and he could undo it in secs and walk away with it, the second one was like a clip and the same thing and yesterday we put on her a half check and i watched him this morning just get it and pull it over her head, bella must have a collar on her at all times, so not using one is not an option, if i was to reprimand my bullie , bella would think she is getting wrong as well and it would knock back all the training we have been doing, anyone have any ideas, apart from gaffertaping my bullies mouth shut
carol

How about trying a comfy, really well-fitting harness instead. I imagine you'd want to check it regularly to make sure it isn't rubbing anywhere, but it might be a bit trickier for the bullie.

Mind you, from what I know of bull terriers, the gaffer tape might save you a whole lots of other problems, like the cost of emergency operations to remove can openers and barbed wire from his tum!

I assume Bella wears a collar indoors and outside. In which case I would try teaching the BT to leave collars alone. Does he have a 'leave' command?

Put a collar on the floor. As soon as he shows interest tell him 'leave' and reward immediately he looks away from it. Put a collar on furniture and repeat. Put collars in all sorts of places and repeat. Do many repetitions until he understands not to touch, and that not touching brings a reward from you.

Once he knows that collars (like books, remote controls, & other "not yours" items) are not toys and he is not allowed to touch them then, should he attempt to touch the collar when it is on Bella, you can say 'leave' in a quiet authoritative tone that will inform him not to touch but will, at the same time, not alarm Bella.

teaching a bull terrier the word leave
carol

It can be done I have seen it myself

Bull Terriers are smart - don't underestimate his intelligence