Pet chips are normally/ almost always a 134kHz , which is close enough to 125kHz, that your Proxmark will be able to read it.
So try your
lf search
if you can’t, feel the location of the chip (normally around the dogs “front shoulders”), you might want to try
lf tune
move the PM3 around until you find the largest voltage drop (best coupling), then send your
lf search
some delay commands, multiple commands might help you also
https://forum.dangerousthings.com/t/handy-dandy-tips-and-tricks/13041/2?u=pilgrimsmaster
https://forum.dangerousthings.com/t/handy-dandy-tips-and-tricks/13041/3?u=pilgrimsmaster