How do I train my dog?

I have a 8 month old Westie. I am trying very hard to housebreak him. It seems that we have a good week then a really bad on. What I would like to accomplish is that he go on the puppy pads when I am not home or if I am unable to take him out. Sometimes I will take him out on a leash long enough for him to pee and poop then we go inside and thirty minutes later he has gone inside my house. It is very hard for me to take him out every hour for twenty mins evryday and also when it rains he will not go or he will be covered in wet dirt and track that all over my house. Any suggestions would be nice.