Joe,
I see that your post is from 6-29-2008...but here is hoping that you check back.
As for the ACE250 it is an excellent machine! I hunt with a Minelab Explorer II that costs much much more but my back up machine is the ACE250...It performs on par with machines twice its cost. You can't go wrong.
Lexington, SC hunting I cannot answer fully. (I live in Lincolnton NC) but parks "prohibiting removal of artifacts" are self explanatory. However here are where I would get my initial ideas.
http://www.lexingtonsc.org/ --- on this site listed source for ""A Pictorial History of Lexington County, SC"
Contact/Join ---Lake Murray Historical Society, Lexington County Historical Society
http://www.lexsc.com/newparks.htm ---- list of parks around Lexington also links to Department of Parks,Streets&Sanation Key Contacts!
http://www.lex-co.com/GIS/Index.html --- arial maps to track property owners, research structures age, plan hunts, see property boundaries.
Oh well best of luck
Raymond.