I remember about a year ago I had anal leakage for about a month, but no smell (at least nobody told me). I could telll that my sphincter muscles were not as closed up as usual. It was really uncomforatble to go to the bathroom several times a day just to wipe. I could actually feel the leaking.
I believe that it was due to a high saturated fat diet (nothing but fast and junk food all day). Since I was leaking slowly, there still might have been a smell, or do the smell come mostly from the gasses?