There are several of these AirTag mounts out there, but this is my betterer take on it. It's lower profile than some, no sharp edges to bother the animal, zero hardware, low / no snag, and designed to be made from TPU for resilience.

Print with the large flat side facing down, this will be the outside face of the holder. The AirTag mounts so that the logo is revealed through the opening showing anyone who might come across an escaped dog that there is an AirTag inside.

The openings are 30mm x 8mm, which squeezes over the large size collars on my 60lb dogs.

If you need smaller, msg me and I can spin a revision for you.