If he is near the coast, it is likely all sand. A liner may be the best option unless the water table is high enough to dig down and use it. But yeah, a pond used like that will need a tough liner.
I would consider doing a little travel to other wake parks and see what they are doing. Keeping the water moving in a large pond using just water pumps will be costly, or require a lot of solar. Aeration less so, but may detract from the experience if not placed well. The aeration may have a positive effect on any smells by keeping anaerobic decomposition to a minimum, where most smells come from.
Good luck!
