Using a lot of "/" in url is not good for SEO optimization.
Not true. And, even if it was, you won't need a lot for this to be an issue.
You can solve this by putting differentiating information in the URLs of locations that occur in more than one country, or in the US, state.
You can put the differentiating information in the URL and appear as a subdirectory.
Or you can just append it to the current location.
In my subdirectory example I demonstrated using the country in the URL and without it. It's up to you to decide what you think is the best from a usability and organizational perspective.