If you havent ran your team on our beautiful beaches yet - here's what to expect. 6" or deeper soft sand as you approach the access points. This last for about 50 to 75 yards. Tough going on a bike and even tougher on a scooter. Generally this portion needs to be walked as it is too much resistance for you and the team.
Once your out on the hard pack - still expect a good amount of resistance. That's the reason you dont see very many bike riders out on the beaches. Expect your pups to want to stop to smell everything. The shells and seaweed everywhere are pretty irresistable. If you get close to the water dont let your pups drink the saltwater IF they try.
I anticipate bikers prob a 4 mile round trip, scooters 2 to 3 mile round trip, and not sure about carts as i have no experience with them. One thing that is helpful is lowering the air pressure in your tires as this decreases the amount of resistance you will experience.
I would also suggest gaining access to water hoses for after the run. You will want to hose off and dry your equipment after each beach run - bring a towel or two for that. Saltwater or just being near the saltwater is killer on equipment. It will rust your stuff quick. Bike chains, gears, rotors, dog collars all will rust if not properly cared for after the run.
Hope that helps some...