tracks, player tracks, car tracks, animal tracks, zombie tracks
tracks in snow/mud deeper/more visible.
tracks decay fastest in grass, slower in dirt, slower in mud, faster with rain/snow/wind.
Substrate - track visibility, track decay, track identification:
Bare dirt - moderate, slow, easy.
Short grass - high, rapid, moderate.
Tall grass - high, moderate, difficult.
Snow - high, slow, high.
Mud - high, slow, moderate.
Sand - high, fast, difficult.
Leaves - moderate, moderate, difficult.
Pavement/rock - very low, slow, very difficult.
Track maker - visibility modifier, decay modifier, identification modifier.
Barefoot - less, faster, easier.
Animal - less, none, easier.
Light shoe -
You get the idea...
This will take the game to an entirely new level.