need advice on a chainguard thingy

howsmyriding27

i have a Giant STP2 with a single roller chain tensioner on the bottom bracket. When I do dirt jumps or big bunny hops etc in a certain gear my chain just bounces off the top of the front cog thing. i was looking to get a chainstay with a roller on the top or a boxguide on the top as well like this: http://www.chainreactioncycles.com/Mode ... delID=8303

any thoughts/advice?