Couple of possible options:
1) Using the 'Ban' feature of Twojeff's Visitor Controller:
http://www.simbology.com/smf/index.php?PHPSESSID=09930f7e1b6b2af9aa3d6b1b4288506e&topic=17.02) Using 'clean' neighborhoods (but read any accompanying or suggested material about such 'hoods, including suggestions for additional hacks to prevent the game from respawning characters, first):
http://kandbdesigns.vndv.com/html/hoods001.html