a mod to an idler

Hey I was wondering if I can get an idler wheel that attaches to both fork bars at the rear so it stays in place like the idler wheels on those phantom bikes. It keeps the idler from moving if it were to come loose. My problem was that I added to much tension to the chain. the damn idler moved into my rear wheel and ripped three spokes out! That's one mistake I dont want to half to repeat.