While ancient walls have been built like yours and still stand, Marcinde's method makes it easier to guarantee that you won't have problems. Your wall looks like it has decent batter, but it cannot be determined from the picture if it's consistent throughout. I think this is one of the most important components of dry-stack retaining wall stability. Keeping batter sufficient throughout will help wall longevity. With greater batter comes greater stability and, personally, I like the look of it as long as it's uniform. You could easily create a wooden triangle with a level attached to gauge the batter uniformly.

Thanks for the input guys.

Marcinde: Your method makes a lot of sense. That was pretty much what I am thinking about doing. Do you use dry stack rocks or concrete blocks?

Yardvaark: I like your idea of the triangle. I actually have more batter than it appears in the photo in most places, but the triangle would improve the uniformity.

GS - it's cheap insurance we put behind ANY type of wall - stacked stone, CMU or poured concrete, timber, or segmental wall blocks.

No advice. Just wanted to admire :)

Thanks all. I am going with the drain pipe and fabric on this one!

Marcide makes a very good point: It is a lot cheaper and a lot less work to put the fabric and pipe in now than to have to rebuild the wall later.

Wish me luck!