Whatever tarp you use make sure and have plenty of bungee cord.
Tie your cord to a stationary object and then to a bungee attached to the tarp.
Pull about 2/3 of the bungees extended stretch when tying off.
This will keep the tarp taught and allow water to run off.
Checkout the awesomeness of our tarp at the ZS SE Campout
I can testify to what Necro is saying,, bungees' make all the difference.
OK, I have seen bungees used with good results but I have been running some form of tarp shelter since the early 70s and never used them. The pros of not using them in my opinion are:
1. You get to learn and use some useful knots and rigging techniques. Learning appropriate knots that you can tie quickly and equally important, untie quickly is a ++ in my opinion.
2. If for some reason you don't have your tarp and bungees you can use these knots and techniques to rig a emergency shelter with plastic sheeting or a "space blanket".
3. Bungees are just one more moving part to pack, loose, break or as I have watched happen, snap you in the face if you hands are cold or wet.
Use them if you want, but my suggestion is to learn and practice the skills that make them a bonus item and not a required item.
To be fair I have never rigged or used a tarp as large as the on in the supplied link, I have only used them for personal shelter.
A picture is worth a 1000 words so here are a couple links for a couple of the many many ways a tarp can be rigged and a couple of useful knots.http://www.youtube.com/watch?v=bjMmla9DSzohttp://www.youtube.com/watch?v=WlyhGDw2osshttp://www.youtube.com/watch?v=eT5z-g3EG7c&feature=relatedhttp://www.youtube.com/watch?v=uiBbktmCGXo
For what it is worth I carry my tarp pre-rigged with cord and prussiks.