We bought the quick release ones as we believe they are safer but this is getting ridiculous. He has a magnet on the collar so only he (and his co-living cat) can get into our house. The collar he has just lost was on him for less than 2 hours. We believe he must be getting them off on purpose as opposed to getting stick somewhere and wriggling free.
He is chipped so the collar was only a way of giving him a door key. No door key no coming in or we change the cat flap and run the risk other the neighbour's bullying cats can come in.
Any other collars worth trying?
Anyone want to buy an expensive furry toy? 
BTW I have asked him where his collars are but he won't tell me.