It could be volume of urine issues due to diabetes, incontinence (though much more common in females than males) unrelated to diabetes or something else.
First thing I'd do is dog a glucose test on his urine, then maybe a urinalysis. I really don't like messing with the incontinence pads on dogs, they don't usually like them and it causes more stress. There are a few medications that are very effective in dealing with incontinence. If he sleeps in the same place without moving much :B, you might try an incontinence bed pad - Walgreens makes a generic version that is pretty large, has a plastic backing and absorbent layers to catch the urine.