Pass Without Trace

(Player's Handbook v.3.5, p. 259)

Level: Druid 1, Ranger 1, Nentyar Hunter 1, Urban Druid 1, Ebonmar Infiltrator 2, Slayer of Domiel 2,
Components: V, S, DF,
Casting Time: 1 standard action
Range: Touch
Target: One creature/level touched
Duration: 1 hour/level (D)
Saving Throw: Will negates (harmless)
Spell Resistance: Yes (harmless)

The subject or subjects can move through any type of terrain—mud, snow, dust, or the like—and leave neither footprints nor scent.
Tracking the subjects is impossible by nonmagical means.