Introduction: Zip-ties for Tensioning
Maybe a "micro-instructable"...
Ever since I saw it described on the Robo3d forums, I've used zip ties for tensioning the timing belts on my printers... if the belt stretches, it's easy to take up the slack, and since the teeth of the belt interlocks with itself, you don't have to worry about the end becoming undone.
If you need to loosen them you end up cutting and replacing them, but that hasn't been a problem for me.
Tip: They come in many colors; make the "loop forming" (never need to be undone) zips a different color than the "tensioning" zip ties. And make sure the tail on the tensioning ones won't run into anything -- if you cut the tail, you can't tension them nearly as easily.