I referenced this design that was mentioned somewhere on here and built a free-standing hammock: http://www.wikihow.com/Pitch-a-Hammock-Without-Trees
It was pretty straight forward, but definitely required some tight, strong guy lines and very solid stakes. Instead of aircraft wire and lag bolts I used 1800lb test 1/2" mule tape and 2' long rebar, hammered nearly all the way in (at an angle). It's cheap stuff, very strong, and doesnt require all the hardware described in the guide (just a few basic knots).
I eyeballed all my measurements, just to see how lazy I could be and still succeed. As a note, I'm 6'3", 225lbs (that's not me in the pics below, that's my 150lb friend).
-two 5' pieces of 3/4" EMT (precut at Home Depot, yay)
-6 pieces of 1/2" thick, 2 foot long rebar
-two 1/4" thick, 2" long bolts
-a nut for each bolt
-about 60 feet of mule tape (or any non-stretchy, very strong line (paracord probably not sufficient).
1. I drilled a 1/4" hole about 3" from the top of each piece of EMT, through both sides, then inserted the bolt and put on the nut.
2. I hammered in 2 pieces of rebar vertically, about 10-12 feet apart (whatever distance makes sense for your hammock), then slid the non-bolted end of each piece of EMT over the vertical rebar (to prevent the bottom of the EMT from shifting around).
3. I took about 20' of mule tape, put a loop at the center (alpine butterfly loop), dropped the loop over a the top of the EMT, and resting on top of the bolt that i slid through earlier.
4. I then hammered in 2 pieces of rebar about 10 feet away from each piece of vertical EMT. The rebar should be positioned about 45 degrees from the line made by your hammock, and it should be hammered in at an angle away from the EMT.
5. With the loose ends of the mule tape (the center being looped over the EMT), I tie them down to the rebar that I just hammered in. I prefer using a trucker's hitch, as that allows a secure attachment, but easy adjustment. Taught line hitches dont seem to work very well with the slippery mule tape, but will likely work with better rope.
6. Repeat steps 3-5 for the other piece of EMT.
7. Use the remaining mule tape/rope to attach your hammock to the top of each piece of EMT. I put a bowline knot in one end, slip it over the EMT, then use another trucker's hitch through the end of my hammock.
8. Give the hammock a very ginger test sit and watch your guylines to see which ones arent tight enough. The EMT should not bend at all if you've got them tight enough. Adjust your lines as necessary to get it drum-tight, then do a few more careful test sits before you fully commit.
All the knots I mentioned above are very simple to learn. Take 20 minutes and learn them (lots of good Youtube videos out there) so none of these things slip on you (else you may get a piece of EMT on the face). The guide above recommends not hanging your hammock too high, which is probably a good idea in case something lets go and you end up on the ground
I found a few things in doing this build:
1. MSR Groundhogs pounded into a grassy lawn aren't anywhere near enough support for the guy lines (duh). They pulled out instantly, and likely will on the playa as well. Rebar or something equivalently strong is critical.
2. My two foot long rebar bent because the load for the lines was not perfectly distributed or the angle from the center EMT point wasn't perfect. It didnt help that the ground was so soft. They cut through the ground about 4 or 5 inches as they bent, but they held all day with various people sitting/swinging in the hammock.
3. If you're going to try to hold two people you will need to use some major anchors for the guylines. 1/2" rebar likely wont cut it for long
4. The EMT may not have been the best choice, especially in a soft yard, as it burrowed several feet into the ground throughout the day (requiring occasional tightening of my lines). Next time i use this in a yard, I'm going to get a 1" thick 4"x4" piece of wood, drill a 1/2" hole through the middle, then slide it over the rebar before I slide my 3/4" EMT over the exposed rebar end (so the EMT rests on a solid base instead of boring into the ground).
5. Mule tape is awesome, though not the best in the world for knots. It held the weight like a champ, however, and barely stretched at all.
6. The guide i referenced above suggests getting square aluminum rods, but I found those to be incredibly expensive compared to EMT. I think EMT would work very well on the playa, as it won't bore in as badly as it did in the yard and being able to slide it over the rebar ensures that the base won't move. In hunting around, I've seen people suggest using wooden dowels (1" at least, I expect) for the vertical support, with a screw/bolt drilled into the bottom to prevent it from moving. I think a wooden dowel would work as long as your lines are very tight so that it doesn't end up taking the load and snapping (or pivoting out of the ground).