1. It was his fault that he didn't put a leash on his dog.

2. He should have walked his dog with a leash on.

3. He should have walked the dog with a leash on his collar.

4. It was his mistake that his didn't tie his dog to the collar. He should have used a dog lead.

5. By mistake, he didn't prepared a dog lead. A dog lead should be put on a dog outside.

6. He didn't keep an eye on the pet when they went for a walk. They were busy talking with each other.

(Would you check the sentences? Thank you.)

2 answers

1. It was his fault that he didn't put a leash on his dog. OK

2. He should have walked his dog with a leash on. With a leash on what? His belt? The dog's collar? Or what?

3. He should have walked the dog with a leash on his collar. OK

4. It was his mistake that his didn't tie the lead to the dog's collar. He should have used a dog lead. I made changes.

5. By mistake, he didn't put the dog on a lead. A dog lead should be put on a dog outside. OK

6. He didn't keep an eye on the pet when they went for a walk. They were busy talking with each other. OK, mostly, but who are "They"?
In #4, "his" should be "he."