I can't make the ignore command works

[bsylvain]

I recently added ember-cli-rails and an ember app to my rails app. It added a folder dedicated to my ember app at the root of my rails project. In my case the folder is named marketadmin.
Since this directory exist, I cannot make guard works because guard does not like the ember folders with tmp files:

Directory: /home/sylvain/dev/placedemarche/marketadmin/tmp/broccoli_merge_trees-output_path-rlX3b4rm.tmp/marketadmin/tests/unit

    is already being watched through: /home/sylvain/dev/placedemarche/marketadmin/tmp/broccoli_persistent_filterbabel__babel_marketadmin-output_path-Nv8C3Z67.tmp/marketadmin/tests/unit

    MORE INFO: https://github.com/guard/listen/wiki/Duplicate-directory-errors
    ** ERROR: directory is already being watched! **

I want to add an ignore command to skip this folder in my guardfile, unfortunately I do not understand how ignore works. Here is the example of the documentation:

ignore %r{^ignored/path/}, /public/

Why does ignore take two arguments ? How do I make it skip /marketadmin/ at the root of my rails folder?