An Entity Question

Ok, this will be a bit rushed because I typed the entire thing and then lost it :O

I have a ctf map where a door will close when either one of the flags is picked up and will only open again if both briefcases are safe in their bases.
to do this I used a math_counter with an initial value of 0, a min value of 0 and a max value of 0. It triggers the lockdown on hitting the max value and opens things up on hitting the min value.
Both briefcases have 3 outputs leading to the counter, which are:

On Pick Up/Add/1
On Return/Subtract/1
On Capture/Subtract/1

It seems to work when testing in single player, but I don't know what it will do in complex situations. Is my logic sound or not? As a final (related) question, what is a good sound to loop for the firing of a rocket engine? I tried using the HL2 sound that steel does, but it gets annoying very fast.

The intel being dropped is not meant to open the passageway. It should only open if both briefcases are safe in their bases, which is why I used on return (the timer running out) and on capture as inputs to subtract from the counter.

Of course, this may turn out to be a terrible idea, but this will be a first time release for me, so I'm mainly doing it to try out the whole taking suggestions and implementing them thing.

I guess if no one knows an answer I can slot it in for a gameday and see if my logic works or not. An answer to the sound question would be good, though.