theres a few options
magic ratio: ie, you find a ratio whereby the chain "just fits" but this is crap as you cant adjust for chain wear.
EBB: you can get an eccentric bottom bracket, that fits in a normal BB shell, but its about 120 quid + the bearings iirc.
spring loaded rear tensioner, like an on one doofer.
ugly, a bit noisy.
Fixed tensioner at the back (gusset bachelor, the dmr versions are rubbish). basicly a roller that pushes the chain up, i find much better than a sprung loaded one, but a minor faff to get the wheel out.
fixed tensioner at the front.
my method of choice, basicly use a roller, like in a chain guide, to push the chain up around the ring to take up the slack.
search for "black spire stinger". this will work even better on the ISGS mounts on the summer season, however they are 20 quid, and dont ALWAYS manage to take up enough slack (i will be using this, but will check how much slack is needed to be taken up first)
it DOES however leave the back end TOTALLY un cluttered, and the wheel is SO easy to drop in and out, and when you drop it in, its automatically tensioned perfectly.