Currently using Northshore heavy-duty side sealing diaper with an additional heavy duty pull up Depends type of garment. It's hard to get them snug enough around the tops of his thighs to prevent leakage. We have to use a medium sized Depends type as the large aren't tight enough around his legs. However the Medium barely come up over his rear because of his large stomach. Any ideas?
Instead of the Depends , Maybe try stretchy spandex bicycle shorts over the brief to keep it close to him and not leak.
One of the problems with that is the briefs (I do not like the term "diaper" for adult incontinence products, but that's me) are backed with a liner that prevents them from leaking. When you put a pull-up type brief over the tab type the tab one will prevent the pull up one from really absorbing anything.
There are liners that you can put inside the tab brief that will absorb more before leaking.
The problem I had with my Husband was skin folds. and he would also do what I called "repositioning" himself. He would "fiddle" and the urine would run down or between skin folds and right out the leg of the brief. didn't matter if it was the pull up or the tab type.
I used washable absorbent pads. I got pretty large ones that absorbed about 1 gall on of fluid. That worked well most of the time. On a chair I would also put a pad. and I would put a pad UNDER the chair just in case it / he really leaked.
There is a product that has been used for women for a while called Pure Wick they have one for men. It is not covered by Medicare. (since it is a medical device it might be able to be taken off on your taxes though you would have to check that out.)
There are also condom catheters. Put on like a condom the urine collects in a typical catheter bag that you would have to empty. There is less of a chance for UTI's with this type of catheter. But if he has dementia most people with dementia do not like "tubes" so there is a good possibility that he will try to pull it off. (better pulling this off than a regular catheter OUT!)
Another option might be looking for a "onesie" that will hold the brief closer to his body so there are fewer gaps where urine can leak.
And one more...There are washable incomitance underwear that might fit him a bit better or ones that can be "adjusted" by someone that sews that would work. Look for "washable incontinence underwear for men" and there are lots of types and you could use one of the absorbent pads/liners with them for extra protection.