You can set the submodule to track a particular branch (requires git 1.8.2+), which is what we are doing with Komodo, or you can reference a particular repository commit (the later requires updating the main repository whenever you want to pull in new changes from the module – i.e. updating the commit hash reference).

git submodule add -b master https://github.com/Komodo/trackchanges.git src/modules/trackchanges