depends on how you've got it setup. if you've got horizontal dropouts, the only way you can lessen tension is by rear wheel position. so i'd expect if you have these the wheel is slipping down the dropouts. solution = chain tension set screws.
if you are running a standard frame solution = chain tensioner off the derailleur hangar.
I think your described setting is an intrinsingly unstable situation (and cannot be solved by chain increasing or relaxing chain tension). I experienced similar problems when I unmounted second the front chain rings plus front derailleur on road bikes for a time trial races (when the second fronting was not needed), chain fell off front chain ring pretty frequently.
If you want to keep the rear cassette shiftability with a stable chain situation up front, I think you need some kind of chain guide up front for example a fixed front derailleur or other chain ring guides. There are simple chain rings (without teeth - like fenders) which are thought to protect legs or pants from the chain, which serve such purpose.
Trek 1000, two mtbs and working on a fixie for commuting.
I just yanked of a couple of links and screwed that bolt on the backside of the RD, generally to keep the pulley wheels off the cassette, all the way in. 1x9, 32t front, 11-32 cassette, X-7 RD. However, I do have a rock ring so I can only say it won't drop in the inside.
If the 32T chainring is pretty center to the cassette or in the middle position of a triple crank, it should work fine. You may get some chain slap/drop on the rougher spots in the higher gears because the amount of slack for the rear derailleur to take up increases as the cog being used gets smaller. It will help to make sure you're running the shortest chain possible: http://sheldonbrown.com/derailer-adjustment.html#chain
It will help to make sure you're running the shortest chain possible
+1, this seems to help alot with my road 1x7. Make sure you do have enough slack for the smallest gear ratio though.
I also have had better luck with the single speed (no ramps) specific chainrings. I am not sure if this is really a factor or if I'm making things up, but I would occasionally drop my chain with a 39t up front - now that I switched it to a 42t I've done about 1k miles without a drop. It seems like the increased number of teeth up front would help hold it on.