Where I sail, we think deep water is about 9-10 ft. Boat draft is roughly 5 ft., so that's lots of room. Groundings happen frequently, but usually no big problem if you aren't going too fast when you hit.
I've had three types of sailboats, so three answers:
In swing keel boats (V24, C22): On the V24, I never locked the keel down. Didn't have a depthfinder. Used crab pots as an guide to where shallow water was and let the swing keel tell me when it was too shallow. The bottom is sand or mud, so the swing keel simply swung back a little when we grounded (rudder was kick-up too so it wouldn't get damaged). When aground, crank up the keel a bit and go another direction (generally going back the way you came in since you aresure water is deeper in that direction).
Fixed fin keel: When grounding, use the engine to twist the boat around so departure could be 180 degrees to original course..i.e. back out the way you came in. Lash the tiller down, put the sails up and harden up, but swing the boom out, then with feet on the rail, put weight on the boom to help heel the boat (don't want to slip here or you might be in the water watching boat sailaway).
Wing Keel: Watch the depth finder very closely. Slow when the water is becoming really shallow so if you touch, it will be a light grounding. Then use engine to twist around 180 degrees so that departure will be in opposite direction from original course ..i.e.back to deep water. Use the rudder and engine to twist the boat back and forth to try to break the suction between the keel and bottom and to gain a little forward motion. Have heard that if you have crew, send them forward to bow to tilt boat fore and aft a bit to help break suction. If you have a rising tide, let that help you also. Wakes from motorboats or moderate waves are also useful to partially lift the boat off the bottom to aid in getting off.