I have all my cats chipped and I have safety collars with tags on all of them, including my ferals. I have an enclosed, cat proof area in my yard for them to go out to from the house. Yes, they have gotten the collars off out there and some I never found!!! I think they may have buried them. But one of my kitties, Katie, has gotten out the back gate several times. Last July she got out and would not let me catch her. She had a great time playing around in the alley and at the neighbors house across the alley. Then she disappeared. I looked everywhere for her. Then the next morning I got a phone call. A person on the next, very busy, street over found her next to his house. She had been hit by a car and couldn't move her back end. He got my name and number from her tag. I rushed her to the vet and after months of healing she has recovered. She had two pelvis fractures and a broken tail, which is now half the length it was. If I didn't have a collar and tag on her, and just relied on the chip, she would probably have been dead when she was finally scanned by the local HS. So, I am a very big believer in safty collars with ID tags on my cats, even if I have to replace them several times a year.