If it's a puncture, you can plug it. Walmart, auto stores, and hardware stores all carry tire plug kits. It's a piece of rubber typically covered in a sticky paste that you insert into the puncture with a simple tool. Be sure to clean the hole first with a file tool (should also come with the kit, and is sometimes on the shaft of the plug tool as a 2-in-1). It's simple and is something you can use on any tire without a tube. If you have a "fancy" wheel barrow that has bicycle type tires (like some of the newer multi-purpose models on the market), your would treat it like a bicycle and change or patch the innertube. There are glue on rubber patch kits available anywhere that sells bikes as well as hardware stores.What do you use to fix yours? This is the first time I’ve had to patch a tire on one.
As for the leak-proof tires (solid foam filled tires that do no rely on air pressure), they can take a beating but I really don't care for them. In my experience they are stiff and don't perform well under heavy loads and over ridges/bumps like curbs or the edge of boards.