30 Minute Desk Catapult (I made it at TechShop)

Step 7: Secure the Rubber Band

Using the staple gun, secure down a rubber band across the tops of the two side supports. Make sure not to actually puncture the rubber band with the staple, as that will severely weaken the rubber band and inevitably make it snap. If you hold the rubber band flat against the wood and center the staple gun over it perpendicularly, it should place the staple so that goes around the rubber band and permanently secures it in place. If the rubber band breaks from extensive use, just staple another one down and it's as good as new.