Negative chain tensioners (pushing up instead of down) work quite well in my experience.
I've got one on my polo bike, stabilized with some cable ties and I've never dropped a chain.
I was going to suggest that too, I used to know several mountain bikers who did that. If I wanted something to race on I think the BB 30 + Beer BB is the best option, nice and clean.
Negative chain tensioners (pushing up instead of down) work quite well in my experience.
I've got one on my polo bike, stabilized with some cable ties and I've never dropped a chain.