You should have to start with Squirtle to get Entei. Start with the worst starter for the worst dog, but no, start with the worst starter for the best dog, how foolish.
It's not going to jump out of a box and walk into your pok�mon. Here's a trick:
Make sure all the pok�mon in your party are at level 49 or under (deposit anything higher).
Use Max Repels until you encounter it. Any Repel based items do not stop the dogs from appearing.
This saves time and.....frustration.
I'm finished here...
Special thanks to Yossy666 for the avatar and signature images.