Had to vote Other, because I think my original 'randomness' rant was a little bit misunderstood. ^^;
It'd be a lot more effective if you choose where to put the Caltrops that deal 3 damage - this way, you won't have it ending up on the end corners of the opponent's board, where it would take several creatures to end up at that point (unlike Flooding, which sweeps the rows clean). Personally, if it worked like this:
Player places the Caltrops in a spot, deals 3 damage once, cannot be removed except via permanent control - that could work.
This way, you could have up to 6 spots with Caltrops on the field, for a cumulative total of 18 damage to their creatures (i.e. - you can spam Caltrops in the same spot to prevent creatures from coming out). It should probably deal less damage for the non-upped version (considering what type of creatures we have in game), say -2 to their HP. The upgraded card can stay the same as is. With the mechanic like that, cards like Fire Shield, Thunderstorm, and Graveyard gain massive synergy.