The slow ride is a test of riding skill.  The basic premise it to selct a limited size track per bike, and the last one to cross the finish line without putting a foot down, going out of bounds, or stopping wins.

The track layout for a good slow race is with lanes one yard wide and twenty yards long.  Some event holders put the lanes side by side, but I personally think for safety there should be a safety area between the lanes.

You can line up two or more slow ride lanes.  I have seen as many as ten riders going at one time.  If you have a small number of competitors two lanes at a time with a tournament style elimination works well.  If you have a bunch of competitors then more lanes to eliminate more riders quickly is needed. 

Basic rules are:
Must not put foot down.
Tires must stay within lane.  If the tire touches the lane line it is out of bounds.
A full stop is not allowed.
May not fall down.
Last rider who's front tire touches the finish line wins.

This event can be done on paved surfaces, dirt, grass, or even on mud.  (yes I have seen slow rides done on mud)  On paved surfaces painted lines are best, but tape, or field talc will work also.  On dirt surfaces I have seen the lanes layed out with string and stakes, but filed marker talc seems to work the best