This is better than our current prison and i would much rather this over the current one, but some feedback points that i have.
The average constable will never get across the bridge meaning they are pretty much forced to have quick peak battles in deer-stands (I'm assuming that is the intended purpose)
No additional cover on the shore so police can't even swim to a safe place in lieu of hatchback rushing.
Heli pad is fully covered (Deer stands don't have a shot on the helipad) and rebels never have to expose themselves so they can load/take off without any risk.
I would suggest adding a small construction/small lighthouse to the south side of the island, Give it a line of sight on the helipad so officers are rewarded for making it to the island instead of just being funneled into the gate for a certain death. Don't give it a height advantage on the deer-stands in prison
Consider throwing a few containers/car wrecks on the main bridge.
Again overall this is much better than our current prison so +1