Whenever you complete a mission you will earn a golden whistles which will give you one chance to smash through a police blockade and continue your run each game.
Liberate Dogs
The more dogs you liberate from their owners the bigger the footprint you will have fanning out behind you and the easier it will be to collect food and raise your speed.
New Dogs
New dogs can be purchased at the 'Title' screen using cash, these dogs each have slightly different abilities which range from being able to accelerate quickly to better top speeds so you should be able to find a top that suits your purpose.
Various Hints
Completing missions earns you golden whistles. Whistles give you one chance to smash through a police blockade and continue your run each game. In short: complete missions!
Liberating dogs from their owners gives you a bigger doggy footprint as they fan out behind you. The more furry pals you have, the easier it is to collect food and raise your speed.
Use your hard-earned cash to buy new dogs from the kennel on the title screen. Each dog has slightly different abilities - from quicker acceleration to better top speeds. Check them out and you might just find the advantage you need.