A proper vulcanizing patch (the kits with glue sold by Park or Rema, for instance) will last forever. You can patch a tube as many times as you care to. I generally patch until the valve fails, the tube splits at the seam, or I'm patching a patch. I had a tube with over 20 patches on it. It died when the tire it was in shed its tread, not because it was over patched.

You might consider more puncture resistant tires, though....

Yeah, I do that too. Just too difficult to keep the patch area clean. I just carry a spare tube and swap it in for the flat one. Then take my time patching the puncture at home in a controlled environment. I use a fine wire-brush attachment on a die grinder to buff the tube, just like they do for auto-tyre repairs. Really makes sure the mould-release on the surface of the tube is removed. Then I apply a drop of vulcanizing fluid to the patch and smear/wiggle the patch over the hole to get an even layer. Then pull off and wait 60-seconds for it to get tacky. Then apply patch and press with thumb for a while. Follow up with a rotary stitcher to make sure the edges are sealed. Takes all of 2-minutes to do the best patching job possible.

I don't use a common technique of using the tip of the glue tube as a brush to smear the glue on. That doesn't apply a perfectly even flat layer across the entire area and due to the time it takes, the 1st areas applied will be too dry while the last areas will still be too wet. That and you end up getting rubber dust and other particles into the tube of glue and contaminate it.

Once fully cured (about 12-24 hours), the patch is permanently bonded to the tube. It cannot be removed without ripping it to bits (or the tube). This patched tube can be used just like a new tube and will last just as long... until the next puncture...