I think this is by far simplest solution to the chain tensioner falling into the wheel.
http://motorbicycling.com/attachments/f3/33037d1296308366-build-two-runs-but-i-need-dsc_1389.jpg
Here is a bunch of pictures that might give you some ideas
http://i63.photobucket.com/albums/h142/Springloaded-too/073-2.jpg
http://i284.photobucket.com/albums/ll9/aquilonian/DSC01683.jpg
http://motorbicycling.com/attachmen...hain-tensioner-suggestions-mini-tensioner.jpg
http://motorbicycling.com/attachmen...-15228d1256983173-im-confused-about-all-chain
http://motorbicycling.com/attachmen...-chain-tensioner-suggestions-12-12-09-006.jpg
http://motorbicycling.com/attachmen...eturn-chain-tensioner-black-lightning-021.jpg
http://motorbicycling.com/attachments/f6/10383d1246643269-spring-return-chain-tensioner-img_2397.jpg
http://motorbicycling.com/attachments/f34/11840d1250275872-chain-tensioner-death-dscf0311.jpg
http://motorbicycling.com/attachments/f34/11840d1250275872-chain-tensioner-death-dscf0311.jpg
http://motorbicycling.com/attachments/f34/11840d1250275872-chain-tensioner-death-dscf0311.jpg
http://motorbicycling.com/attachments/f11/19999d1265485665-using-derailer-tensioner-img_0034.jpg
http://motorbicycling.com/attachments/f3/33037d1296308366-build-two-runs-but-i-need-dsc_1389.jpg
Here is a bunch of pictures that might give you some ideas
http://i63.photobucket.com/albums/h142/Springloaded-too/073-2.jpg
http://i284.photobucket.com/albums/ll9/aquilonian/DSC01683.jpg
http://motorbicycling.com/attachmen...hain-tensioner-suggestions-mini-tensioner.jpg
http://motorbicycling.com/attachmen...-15228d1256983173-im-confused-about-all-chain
http://motorbicycling.com/attachmen...-chain-tensioner-suggestions-12-12-09-006.jpg
http://motorbicycling.com/attachmen...eturn-chain-tensioner-black-lightning-021.jpg
http://motorbicycling.com/attachments/f6/10383d1246643269-spring-return-chain-tensioner-img_2397.jpg
http://motorbicycling.com/attachments/f34/11840d1250275872-chain-tensioner-death-dscf0311.jpg
http://motorbicycling.com/attachments/f34/11840d1250275872-chain-tensioner-death-dscf0311.jpg
http://motorbicycling.com/attachments/f34/11840d1250275872-chain-tensioner-death-dscf0311.jpg
http://motorbicycling.com/attachments/f11/19999d1265485665-using-derailer-tensioner-img_0034.jpg