1) If you can catch it digging in the sand by hand, it ain't a crab. It's either a clam, or a rock.
2) CR is correct about Sammy's videos. I would disagree that you need to fish at high tide. The perch are there and you can catch them at any point in the tide. Our beaches do not tend to be very steep, so yeah you want to look for places with a depression, or a dip between the shore and a little bit of a sand bar farther out. Above all, avoid conditions and locations where there is a sideways rip, because you can cast at a 45* angle one direction and in 60 seconds find your rig has been pushed just as far in the other direction, and all the way inshore. I would say fish in the less extreme tides.