Plugs work good. When they do fail it's not a sudden loss of air pressure, just a slow leak. So not much danger.
Plug a tire with pressure in it. If your kit came with a ream(any good kit does), ream the hole out good creating a rough surface the adhesive can stick to. Leave the ream in the hole to hold the air in. You want it at or above operating psi. Have your plug ready, pull the ream out and quickly push the middle of the plug in folding the plug back on itself. You'll have both ends facing out with a loop on the inside. Cut the excess and check for leaks with soapy water. That will pretty much never come out.