new trap: hidden wall

we all leave an opening in our walls to lure giants and other troops in with spring and giant bombs waiting for them, how about having a trap that is an invisible wall up till the point that someone reaches it's trigger radius - once revealed it would act as a regular wall that the attacking army would need to break through. and if revealed it would need to be re-armed for it to work again (if not re-armed would be just an opening). like regular walls it would be purchased at an entry level for a given price and then upgraded to higher levels.

Name of Trap: Hidden Wall
Trigger radius: 2 Tiles
Price: 200 DE
Rearm Cost: 200 DE
Maximum Available: 1 at TH8, 2 at TH9, 4 at TH10 (max)

Level 1 Hitpoints: 2500 (similar to Level 7 regular wall)

Upgrade to Level 2: unlocks at TH9
Cost: 10000 DE
Time: 4 days
Hitpoints: 2500+1500 (similar to Level 9 regular wall)
Rearm Cost: 200+100 DE

Upgrade to Level 3: unlocks at TH10
Cost: 50000 DE
Time: 10 days
Hitpoints: 4000+3000 (similar to Level 11 regular wall)
Rearm Cost: 300+200 DE