another method ive heard of, is to tape off the entire tank with visqueen and use a large air pump placed outside to pump air into the "tent" youve made for you aquarium, this gives this tent a positive pressure and you just make a small, but still large enough opening for the air to escape. in doing so this allows for a source of constant fresh air to be given to the aquarium and by keeping a positive pressure inside the "tent" no poisons are able to enter in.
however the downsides to this method are using a large enough air pump to supply a adequate amount of air, as well as long enough tubing.
just a method ive heard of being used. never used it, but i believe some in the club have.
we'll see if anyone comments on this method.