Two choices...flush him or keep him in his own tank...kinda fun to watch, but you have to sacrificea damsel to him now and again. 10gal tank for isolation works well.
I did a stake out, (don’t ask how long, it was a while) just sat there looking at the rock and he moved from one rock to the other. I took the whole rock out that he was in and chased him out with a straw.
Call your nearby LFS - they might take him off your hands and then you could save a life, maybe even get some credit for him. My LFS occasionally sells mantis shrimp but I don't know if they buy them to sell or just get them out of their own LR.
