[GeoKrpan]

Use a 44 tooth chainring.
There is more tension on the chain and more chainring teeth engaged with the chain and it won't fall off.
I just got done 1x9ing my Jamis Exile and it works perfectly WITHOUT any chain keeper oner thigamajig.

The gear inches with Schwalbe Big Apple 2.35s and an 11-34 cassette range from 37.5 to 116.
If I were using a 32 tooth chainring the gear inches would be 27.3 to 84.4.

The single speeders I ride with usually use a 32 chainring and a 22 cog which translates to 42.2 gear inches. Thus, at 37.5 gear inches, I am geared lower, and THEY climb EVERYTHING.

I know this won't work for everybody. I use the Exile as an "adventure bike". In other words, not strictly as a mountain bike. I have another 29er with a triple crank.
If you're using your 1x9 in the same manner as I do then this might be a good tip for you.
37.5 gear inches is more than plenty low enough to climb any road and 116 gear inches is as large as a road bike.

 

[mvi]

I use a old front derrailleur and never dropped the chain with a single 39T.

 

[GeoKrpan]

I use a old front derrailleur and never dropped the chain with a single 39T.

Nothing wrong with that, a good sensible thing to do.
However, it looks much nicer without the "front derailleur to nowhere".

 

[edbraunbeck]

For $12 the N-Gear Jump Stop works great! Nick will even ship it to you and let you try it. Then you pay him if it works. Great policy if you ask me.

http://www.gvtc.com/~ngear/index.html

 

[mtnfiend]

I was using a long cage XT derailleur with a N-Stop for a long while and was dropping my chain all the time. I was about to get a Rholoff chain thingy as a last ditch effort. I needed a new rear derailleur after an incident with a branch in Sedona, so I got a mid-cage SRAM x.9. The shorter cage, stronger feeling spring, and slightly shorter chain seem to have done the trick. I haven't dropped my chain since in stalling the new set up.

 

[edbraunbeck]

Niner recommended a short-cage. I've had the bike for a little while but the three rides have been flawless so far.