My son pees so much at night that even when I have him wear two depends he still wakes up drenched. Any ideas?

My son is on medications for his disabilities that make him pee the bed at night. He is six years ol weighing ninety pounds. He has been doing this for about two years now, but as he is getting bigger so is the volume of his urine. I have tried Goodnights and Underjams. Neither of them work for him. I have tried different brands of adult disposable underwear also like Depends and Attends. I have him wear two at night and he still pees through them waking up drenched and so is the bed. I have to wash his blanket, quilt, and sheets daily. I am wondering if anyone has any other ideas I can use to help him stay drier at night, or atleast something to absorb the pee. Those bedding protector pads like Chucks don't work for him because he moves too much while he is sleeping so they don't stay in place