Beelzy:
Way too time-consuming, although "Beelzebub" is an awesome psudonym...."Lord of the Flies".

Past experience has shown that a double strip of duct tape will give you a seam that will hold even if the polythene is compromised. Neither strip of tape can be peeled away, because the partner strip stops any movement.

At the lower edge (floor) of the haunt, lay your membrane flat. Pull a continuous length of Duct Tape along the edge, fixing it to the floor. Fold over and repeat. Lift the membrane up to the ceiling. You will need a minimum of two assistants for this. If the membrane is not already cut to height, do so now. Repeat the procedure that was followed at the floor.

This will give you a cheap, fast and fool-proof wall, but be aware that some effort will be needed to remove it.

Wolfman