if you use a long-cage derailer it will take up most of the slack. was planning to add an extra tensioner on the lower jockey wheel a la steve parry. however havent got around to that as it has worked well without it, this because it turns out the chain rests itself in a predictable way on the derailer.
if you lay the bike on the side the chain might work itself off. but i hardly ever do that, so the parry solution has been put on hold. in my case it would suffice with a shorter tensioner than pictured. an alternative solution is using a bigger jockey wheel, but the chain is close to the ground as it is.