Well lol i am rather new to mapping in goldsource (made just 1½ maps).
But i found a solution to your problem.
So you need something to reset every round start, so a func_breakable restarts every round.
My idea is to coat your breakable box with a trigger_multiple which will trigger a multi_manger, this multi_manager triggers an env_beam then triggers another multi_manger with delay of 1 sec that will switch the env beam off.
This env_beam starts from target1 to target2, in between these target lies another "breakable box" having 1 strength. When the player activates the trigger_multiple it switches on the env_beam doing 99999 dmg to the "breakable box",hence breaking it, which targets your breakable box breaking it.
Now the player can pass number of times nothing will be trigger again because the "breakable box" have been destroyed which cuts the link to your box.
Well if its not clear i did a test map (forgot to put light).http://www.mediafire.com/?k5847qdciv6mqm7