>>>>I would use hardware cloth, not sure what you might call it in Singapore. It's a metal screen fairly stiff, with square holes in it about 6mm each. Thinking that you have a standard 10 gallon tank it's measurements should be about 51cmx25.5cm. Cut a piece of hardware cloth 5cm larger in each dimension. Then cut a square out of each corner 2.5cm and fold the screen down in line with cutouts. You should have a cover that looks like and upside down tray. If the dimensions are right this should fit over the top of your aquarium giving you a simple cover. You can stitch the corners together with short bits of wire and use rocks or books to weigh it down. It's not fancy but it's quick and easy and you don't need many tools. Just some metal snips or good utility scissors to cut the hardware cloth. You should be able to find this at a hardware store or lumberyard.
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>>Ahhh... a top weighted down with books or rocks... I'll bet more herps have escaped from this sort of cage than any other! Personally, I'd suggest building a wood frame around the top, affixing it with some sort of adhesive, and then some sort of sliding or hinged top within that frame. Not sure that the original poster has the tools or skills to make that happen, however.
You can make a tight fiting wood frame and attach the wire cloth or screen door screen directly to it. Reinforce the corners and make it fight snug (so you have to push alittle to get it on) This will keep your snake safe and happy NO ROICKS OR BOOKS as stated before snakes get through cheesy tops like that.
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Chris, my wife Mary
a dog, two cats, two birds, four snakes
oh and three kids