-- Last Updated: Sep-11-12 4:52 PM EST --
Not sure, but I'm guessing some of those nearby rule/reg governed bodies of water you allude to might be some of Howard County's or W.S.S.C.'s governed lakes, i.e. Triadelphia Reservoir or Centennial Lake, to mention a few.
Well, right up the U.S.29 to Route 99 path from your Gem of the Ocean zip, in the Patapsco Valley State Park, you can slip on down Daniels Road to the Patapsco River, there where it pools behind the Daniels Dam, and, avoiding a few silting accretions which might tug at your skeggy-finned bottom, have yourself at least a 2/3rd mile upriver run (perhaps a mile and a third, if the rains ever lift the nearby gage back into the 2-foot reading realm) against soft current. Seldom that crowded on the water (saw a few kayakers and one SUPer there this past Sunday), with usually most folks there to hike or fish the rivers banks and woodland trails.
And the rules aren't too bad! Sunup to sundown (I've slipped on in to this takeout a few times as dusk waned), no PFD regs, and just keep your dog on a leash (not sure how that works on a paddle board) whilst foregoing alcohol's consumption. (I usually just tell the ranger the damn dog chewed through his leash and went off on his beer run before returning. But then, I'm a low-key irrational Duckhead of a canoodledlist, too.)
Anyway, for a quickly reached place to practice your SUP maneuvers, with the occasional side benefit of osprey and heron and other wildlife companions, it would be a fair choice.