Instructions
Proceed through the game until you have defeated the Elite Four and earned the National Dex. This unlocks the sixth region in the Safari Zone, where Houndour lives.
Travel to the Safari Zone. It is north of Route 121.
Walk north through the Safari Zone until you can go right. Take the right-hand path.
Veer north when you reach the lake. Eventually you will come across small hills backed by a mountain. This is Houndour's domain.
Wander this area until you encounter a Houndour. Attack him until his health meter turns yellow or red, and then throw pokeballs until you catch him.