To defend against dog ambushes you need to play as Carl (some people have said they could not unlock this achievement with Russell – I played as Carl to be safe). The dogs will growl before they attack. As they attack press the
Button to knock them back. Do this twice to each dog and you will stun it (the dog should have a circular white icon above it’s head) giving you the opportunity to get rid of the dog. Walk close to the stunned dog and when the
Button symbol appears above your head press the button. Carl will tie a balloon around the dog causing it to float away and Russell will throw a squeaky toy. If you press the
Button before the symbol shows up above your head you will hit the dog and you will have to stun it again. There are more than enough dog ambushes spread throughout the game and you should unlock this by Level 7.