I think (and that could be dangerous)
If you set up the tentioner so that it is hinged to pivit,,, yet have a stop built into the botton so that it cannot spring down past normal setting ,,and a safty bar that is attatched to the pivet bar/wheel that extends below the chain stay and above the seat stay on the out-side ,and can move w/the tentioner wheel,,,,add a spring from the tention wheel piviting bar to the seat stay,,,,,,It looks good in my idea note book,and solves the chain allowing too much slack when starting the motor ,and keeps the tention wheel out of the spokes w/the safty bar ,while keeping spring tention against the lower chain playing while moving foward !!!