Instead of petting him, why not pick him up?
When hes in his territory, its his territory. He needs to feel safe there, so he will defend what hes got. He may not understand "getting pet", so he takes it as a simple threat to his relaxation.
If you just pick him up, he will understand, he is being handled now, he realizes hes not longer flat footed in his own home.
Most of my younger BPs are pretty tame, but they dont like it when you just mess with them in their home. Some will hiss, others puff and breathe heavy, others will strike. You got to pick them up to let them know who's boss kind of.
With a bunch of my older BPs I'd feel safe enough to pet them in their enclosure and not worry about them biting or getting agitated, they are more like dogs nowadays. Attention seekers
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