How can you catch the legondary dogs?

You can catch one of the dogs per game, depending on your starter. If you chose Bulbasaur, you will find Entei. If you started with Charmander, you will find Suicune. If you started with Squirtle, you will find Raikou. They will roam around the grassy routes of Kanto and you will have to search them out.

To catch a Legendary Dog, you must defeat the Elite Four and catch 60 pokemon. Get your National Pokedex from Proffessor Oak, and go out into Kanto. Depending on which starting Pokemon you chose, you'll get a certain dog.

Charmander: You'll get Suicune.
Bulbasaur: You'll get Entei.
Squirtle: You'll get Raikou.

It depends on your starter.... Squirtle = Raikou
Bulbasaur = Entei
Charmender = Suicune

After you beat the elite 4 and got the national pokedex...the legendary beast will appear depending on your starter pokemon.

You can only catch one Legendary Dog. The dog depends on your starter, it type trumphs your starter. Here is the chart:

Your Starter Dog
------------ ---------
Charmander Suicune
Squirtle Raikou
Bulbasaur Entei

After you beat the Elite Four, the dog will then roam around Kanto. No sea, no caves, just the wild grass. Search the grass and you can find the dog at Level Fourty.

You need to beat the four leage and then when you walk around on Kento not the Sevi Islands you will eventually find one but I don't know if you can get them all.