In general, mechanical raking beach cleaners are excellent at removing rocks and shell from the beach, because of the variety of sizes the tines can capture. As you can see in the pictures, the tines are large and strong enough to pick large rocks from the sand but dense enough to remove tiny stones and shells without removing sand.
As a specific example, the SURF RAKE, in particular, excels and rock and shell removal. The Barber TURF RAKE is one of the leading machines in the rock and stone-picking market, and, thanks to Barber's patented S-belt, SURF RAKE beach cleaners are optimized to use this technology in the sand and pick up rocks as large as a football and stones as small as 3/8". Additionally, with a dump capacity of up to 4400 lbs (1,814 kg), no amount of rock or stone will prevent a full hopper from unloading into a tall dumpster or truck. The operator can consistently fill the beach cleaner's hopper to the top regardless of the density of its contents, which results in fewer dumps and greater efficiency.