An alternative/addition to caltrops could be some kind of sticky substance to be thrown at the feet of the target. Be it bitumen, tar, creosote. All are black and are sticky. The problem with them is in regards to temperature, so what it would mean in game is that it could be purchased warm, soft and sticky and after a while it goes harder and subsequently less sticky.
Effect could be fresh tar 2 seconds delay on leaving the room. Lukewarm 1 second and cold no effect.
I'd see some kind of check against dexterity to avoid it, and an option to remove boots to re-roll with better chances (you're aware of the stuff this time around). I'd see the boots stuck on the ground if successfull roll.
Lighting it on fire is an option worth considering too.
