Mostly just limit what rock they are growing on (they won't grow on substrate) or to trim them back. You can cut them off the rock since they grow in a mat or you can frag the rock out and replace it with a different one.
GSP grows quite fast if it's happy. You can cut a piece of the mat and remove it from the rock or from any problem areas. Use a sharp blade, like a scalpel, and make clean cuts. Then, you can use wedding veil to hold it down to a plug or a piece of LR rubble until it attaches. Then, spread some frags around to fellow hobbyists... frag karma comes back around. ;D
Thanks a ton kloseo! Business is pretty good so far, but I don't really see us getting into the salty side of business. There are just so many great SW only stores around here... surprisingly, it's FW stores that are really lacking in this area!