New trap - cage

Cage :-

It is a trap which triggers on a troop walking on it.
A circle of wall rises in a 3x3 radius with hitpoints of 1500.
The trapped troops have to break the walls first and then continue to battle..
The cost would 700 dark elixir and with each upgrade the hitpoints of the wall increase by 200.
The max level is 3 and the rearm cost would be 70 dark elixir.
Level 2 upgrade costs 5000 dark elixir and rearm would be 100.
Level 3 upgrade costs 15000 dark elixir and rearm would be 200.
Only 2 of them would be allowed per village.
It cannot catch flying troops.
It cannot trap wall breakers.
Archers can shoot above its walls.
The nearby defense buildings can shoot the trapped troops.
If the troops dont get out in 15 seconds... They will be trapped forever or blast off..something like that..
Please consider this idea.

If its a trap then it have to be hidden. But by ur idea it will need a large amount of space, which will help players to predict where the trap is. So it won't be handy. And it costs more than inferno tower!! Who wants it!? .. even without its cost it will drain a decent amount of space. It won't be necessary

Is there a limit as to the capacity of what this cage could catch or no?