Caltrops (4e Equipment)
From D&D Wiki
Caltrops are small pyramid-shaped metal spikes. They can be dropped into a square adjacent to you, or gathered back up, as a standard action.
Any creature moving on the caltrops must either treat the square as difficult terrain or become slowed (save ends). Running creatures must become slowed.
A bag of caltrops for one use costs 10 gp and weighs 1 lb.