"I Am Sheriff" + add more guards. End of discussion. This is all typical factioning IMO. You place the guards, you risk them being lured, and your cities silver being drained. Welcome to Felucia.
Actually, under these circumstances faction guards should recall (literally) back to their home location(s). Clearly this is not working.
If they get lured out of GZ, they will no longer be under command. Rather, you can't get the targeting cursor for using commands as Sheriff, outside GZ. I did find that you could 'precast' "you are fired" and run out of GZ with the target cursor and click them to remove them. HateCrime, you cannot summon more guards while others are 'somewhere' else. There's a finite number available as I'm sure you're aware.