Nice little game. I like the sprites but the background would have been better as a tiled texture of sand. The gun sound effect didn't sound right, but other than that it was fine.
Took me a while to realise I could actually move lol. I thought I had to stay in the centre and rotate like I was drunk :)
I couldn't work out how to repair the fences though, I click the button and it takes 20 of me gold but nothing happens.
I like the idea of falling back to a more defensible position.
After a while though I found the game too easy, because I realised you could use 50 points to upgrade your pistol for a short while, and in that time you can easily get well over 100 points, so you can just constantly upgrade and never lose.
Also as the other commentator mentioned, the game did want to get through my firewall, so I imagine that's some nosey Unreal thing, but I just blocked it and the game ran fine.
Great work though.