If you get really wound up and just want to complete it, the way i did it is slightly exploity. If you go to the dodgems on your right and walk over it and drop down behind it, you're then sandwiched between the dodgems platform and the fence. To get to you the enemy has to go round the platform, it's the only way they know how. So you can watch them coming and snipe them as they come , or when they finally get round, jus lean round the edge of the platform and snipe em in a line.
I tried for aaagess to try and do it properly by finding a nice bit of hill, but i always, always got mauled by a dog, i can never knife fast enuf to kill it :(
:D
Biggest complaint is the fact the enemy keeps coming until you reach a certain point like in all COD games. I think it's a bad decision tbh. It makes finding a clever point to pick the enemy off pointless as once you begin to move up, they've all "respawned".