There's a nice idea behind this, the concept of a dog keeping their owner safe is very cute (even if their death is inevitable). However it is very easy to avoid the vehicles by running in a diagonal direction until you hit a corner and then reverse the direction. This could possibly be remedied by restricting the player to the bounds of the screen (or a similar sized area). Apart from that though, it's a lovely little game, and there's a lot of potential here. Great job!