There is lots of diving around here, unfortunately most of it is 'blackwater diving'. I've dove on the WWI sub S-49 off of point patience in the Patuxent River several times. It is down at around 120 feet with visibility ranging from 6inches to a couple of feet and lots of monofiliment.
I've also dove the German U-boat, U-1105, off of Piney Point in the Potomac a few times. It is not quite as deep as the WWI sub, but visibilities are about the same. Currents are usually a non-issue if you plan your dives accordingly.
As far as trying to spook a student in a pool, not a good idea. You can have a lung over-expansion injury in as little as 4 feet of water, with the greatest pressure changes being in the last 33 feet of water. I do, as per standards, a valve shut off exercise while students are kneeling in the shallow end of the pool, and also regulator removal and recovery underwater. You don't want to panic a student and have them swear off diving forever.