Advice on running ground bus wires

You don't need to loop back.  I did so  only to have quick access to ground under my main lines.  I used 12 gauge with 18 gauge feeders to the track

I have a single run of 12 g bare copper wire salvaged from a construction project that runs probably 40 feet in total.  Not a loop, just a single strand, feeders are dropped down to this and soldered directly to this ground.  The rest of the power supplies are probably 14 g color coded.  
The layout isn't all that deep except for return loops so this common ground is kept within 12 inches of the table edge.

Thanks for the helpful replies.  That was my preference - 12 g dead end runs for the ground bus wires, with 18 g feeder wires - but just wanted to check in with the experts.  I will have color coded power wires of different voltages to operate various items (switches, accessories, lights, etc), but wanted some advice on the common ground.

I have been operating trains since my teen years (over 50 years ago), but now building the "dream" layout with lots of new experiences. Want to keep it as a dream of fun experiences...not a nightmare of mistakes. So far so good!

Thanks again,

Michael