Watch out for this if you try it in a city, because you could run afoul of bylaws and angry neighbours. In Surrey, British Columbia, a family tried doing this. They had piled up bark mulch and manure, and one of their neighbours complained to the city, which then told the family to remove the piles under Surrey's Unsightly Premises Bylaw. I don't know the outcome (I haven't found any articles after this point) but if you start piling bark mulch in your back yard, make sure you don't piss off your neighbours doing it.
I would also add that there are height restrictions on "fences" as well. At six feet, there is a setback consideration in the front in my city at least.
That said at the bottom of the article:
My HOA won't allow anything like that, what do I do? (my neighbors would freak out, what do I do?)
There are many possibilities. Some people dig a trench five feet deep, fill that with organic matter and have something that is either flush with the surface or it appears to be only one foot tall (which is in the comfort zone of neighbors and HOA folk). Other people will build something that is 18 inches high the first year, and add a foot each year. Still others will have so many neighbors build them all at once that it is difficult the buck the tide. And then there is always the back yard.
http://blogs.vancouversun.com/2013/10/03/surrey-takes-action...