Ultimately any anti-theft device is fallible, the point of them is to create deterrence by increasing the hassle and effort/time involved in stealing whatever it is successfully

Which will deter crimes of opportunity and make more professional/targeted thieves consider easier targets

For example with bike locks even super high end ones can eventually be cut with an angle grinder, but that takes time and draws lots of attention, so why not go for a bike with a lock that can be shimmied or has none at all

In the case of an AirTag or another similarish RFID/GPS/wideband/lojack tracker type devices you'd need a Faraday cage large enough to hold the thing, which in the case of say a small electronic device like a phone may not be very hard for an fairly dedicated and decently equipped thief, but to steal a dog I assume you'd need a van with the back compartment Faraday'd and/or a Kennel with the same(I don't actually know how pet implants work so this is just my educated guesses to illustrate my point)