Help! Dog keeps pulling hard on leash and my arms hurt from it.

I’m a pet sitter and I walk a dog Monday-Friday for a client.

The pup is very sweet and a pleasure to watch… Until it’s time to actually take her for a walk.

The pup is a medium sized pitty mix, who probably weighs around 40-50 pounds.

My client lives in an apartment since I started working with her over 2 years ago, so going for walks is nothing new.

My client lives on the 3rd floor of her apartment building, and the pup has pulled when going up and down the stairs (which I’m used to, so I know to really brace myself before approaching them).

This dog pulls every time we go for a walk, and I’m not sure how to help lessen this. I’m working with the owner to train the pup not to pull, and there are times she seems to be getting it, but not for long.

I’ve tried the method of stopping until the leash goes slack then continuing the walk, and turning the opposite way when she pulls. The pup seems to think it’s a game and will start running/ pulling harder when this goes on for a little bit.

The pup is on a harness, which gives her more strength to pull. I’ve suggested a Gentle Leader for the pup, as my parent’s dog uses one and it has drastically stopped the pulling.

Is there anything else I can do to stop her from pulling so much?