hard to advise without knowing more about your game or being familiar with urban rivals.
You tried one thing, and it didn't work, I suggest trying a bunch more, even if the idea seems silly or unlikely to work. you may stumble across a good method or get inspired
first ideas that came to mind for placing cards; maybe write conditions into the cards, so they can be placed anytime if a condition is met. or maybe let them be placed in any turn, but they have a time delay, like you would place a card face down and could only "activate" it by flipping it on a conequent turn.
Thanks for the reply. I've tried about 6 ideas so far, and only one has worked in the way I want.
Basically cards can be played before each round, and are activated similar to traps. These are played before each round, and are activated by certain actions.