Are there any adult diapers that provide strong protection from leaks?

If the problem is that the products you've tried don't hold enough then there are premium heavy duty overnight briefs like tranquility, abena, north shore and others. There are booster pads that can be used inside regular briefs, but with the added cost I think you are probably better off with a premium brand.
Also try placing either washable or disposable pads on furniture as well as a leak proof mattress cover on the bed.
Since you are caring for your father another thing to be aware of is making sure his penis is adequately tucked into the brief.