haha I found a technique! on the second mission (the hospital) you can park your buggy just on the narrow entrance of the new garage then you can just bust out all zombies without harming you, well you still have to deal with the birds and the gunned zombies.
 "Edmus"){kind=icon}
 "Search for games & more"){kind=icon}
 "Doodle God 2"){kind=icon}
 "Epic Combo!"){kind=icon}
 "UPGRADE COMPLETE!"){kind=icon}
 "Ghostscape 2 - The Cabin"){kind=icon}
 "zombie horde 3"){kind=icon}