How to do fill once with execute

I am working on a theme park and i want to make it so that when you walk up to the exit you cant go into the ride through there but if youre exiting you can. I have tried execute if entity @a positioned (cordinates of trigger) run fill (where the barrier is) barrier and the other way around if your exiting it. I put the command into a repeating command block and turned it on always active. But i ran into the problem that once you step on the trigger cordinates, it just fills it and keeps repeating the fill command over and over instead of just running it once. I also tried and impulse command block on a repeating clock, or a repeating command block on a repeating clock, but nothing has worked.