Automatically track remote when pushing untracked branch

It would be great to have an option to automatically check the "track" option when pushing an untracked branch to a remote repo.

I often create new topic branches locally, push them to GitHub, and create pull requests. Unfortunately, I usually forget to click the "track" option, so when the PR gets merged and I delete the remote branch, I have to manually go back and clean up my local branches.

I can see how tracking by default could be bad when pushing to remotes that are not entirely under your control. Someone else could delete a branch you are interested in and the deletion would propagate to your local repo during fetch. Maybe the pref could be repo-specific, though that creates another layer of complexity.