I personally prefer sand over anything else including mats. The sand seems to support them better than anything else. It is also very easy to clean out manure and the urine drains right through so the stall stays dryer and there is no need for shavings. Definatley more cost effective than mats and shavings or even just a plain dirt stall.

I did have stall mats at one time, they were just layed on top of a compacted dirt stall floor. The horses would periodically flip up a corner or even shift the mats. Although I have heard some good things about that stall skin product.

Good luck