I just never really have a problem with my Omnipod, but I do with my Dexcom. So I can tell you what works with it! The first Dexcom started falling off the first day I wore it. So I started using Skin Tac and at first I would put it over the top of tape too. But then I found touching up under the edges that were peeling up with a q tip worked better. But then I started to restart them and wear them longer, so I needed more help. Dexcom has overpatches which I wasn't impressed with until I applied more Skin Tac under the overpatch when putting the overpatch over the Dexcom. They almost never even peel up on the edges now and I wear them 20 days plus.
I know when I swim for a couple hours though I have to be more careful of my Omnipod because it isn't adhered well when it's wet. Once it's dry again it seems fine. Grif Grips has some wonderful overpatches for the Omnipod and other devices in different strengths, but you might try applying more Skin Tac before you apply them. I couldn't keep using them for my Dexcom because I was allergic to the adhesive, but they worked great!