Done many patches nothing never failed except once when I missed the hole. I put a smaller patch over that and I used it for a couple of years. I used always used generic cheap patches and never had a problem. No alcohol either just scratched a little surface away. No road bikes with slim tires and ultra high pressures though.

If you get punctures very often then it's time to rethink your tires or riding style. Although using very crappy worn tires increases the speed and skill fixing patches. Maybe using old tires for this reason is not a good idea otherwise.