Kathy and I spent the weekend at Orange Beach, Alabama in my parents condo. My mother is a master shell hunter. She has found tens of thousands of beautiful shells over the years. She spends hours walking the beaches picking up shells, coral, sand dollars and anything else that washes up on the beach. She even gathers abandoned T-shirts and beach towels. No relaxing with a good book for her. When she hits the beach it's all work.
She finds most of her shells by digging. Most beach tourists would love to take home just a few good shells like she finds, but very think to dig. Unless you pay a little attention to detail, digging is not likely to produce much. Find a good spot, and you can take home a bag full.
The majority of the good shells that are found digging at the Alabama Gulf Coast get deposited there by dredging. The hurricanes and tropical storms of the last few years took away most of the sand and leveled the dunes. The State of Alabama has spent millions of dollars putting the sand back, most of it by dredging the sea. Tons of sand has been deposited on the beach, and along with it all of the stuff small enough to get sucked up the dredging pipes.
Occasionally a good spot for digging can be found just by looking for spots where somebody else has dug. Most people are good about filling in their holes, but unless it has recently been smooved over by beach maintenance workers, you will still be able to spot depressions in the sand. Try first at the edges that haven't been dug and work your way back away from the depression. Lots of small broken shells on the surface indicates that there are probably better, unbroken shells underneath.
Don't dig near the shore line in the space that high tide covers. Move back aways. Don't dig in the dunes. That's not good for the beach and will get you in trouble.
You don't need big garden tools to dig in soft sand. Small tools work fine and are less likely to damage shells.
It's permissable to dig small holes on the Alabama beaches. It's not a lot different than building sand castles, Whether you're digging for holes, or building sand castles, fill in your holes when you're done. Holes on the beach can be dangerous.