I cant figure out how to make a hero unchoosable after someone picks it before you

I have the wisps and you move then over a portal in front of the hero to pick it, but i dont want the whole team picking the same hero, is there a way i can limit the hero used to 1, or delete the trigger after its been used?

Simply add this action to the beginning of your trigger:

Trigger - Turn off (this trigger)

When someone moves there and gets the hero, the trigger is turned off, so no one else will be able to select it.

you probally have tirggers like

Event-unit enters region (paladin)

Action-create 1 paladin for owner of entering unit

just add a new action so it will be like

Event-unit enters region (paladin)

Action-create 1 paladin for owner of entering unit
Action-trigger-turn off this trigger

Exactly what I said. :) Though you want to make sure that your first action is turning off the trigger. This greatly decreases the chance that 2 ppl set off the same trigger when they both enter at the same time. By turning off the trigger as your first action, the rest of the actions will continue to be executed, but it will no longer be active for others.

I used Circles of Power on the ground in front of my heros and a Unit Within Range trigger for character selection. When someone chooses one, right as I would create that hero for the player, I simultaneously delete the unit (the circle of power unit) so that nobody else could step on it (come within range of it). I also feel the visual feedback of seeing the circle absent in front of the hero will help the players to instantly understand that the hero is now "taken" and no longer available.

Just an option...