This is a little late. The Roadmate 300,
360, 500,
700 and
760 all use the same antenna design. There is a notch on the post to which the antenna attaches. If you rotate all the way to the stop, a key on the antenna lines up with the notch on the post. You can then easily pull the antenna off the post. To prevent the antenna from coming loose on its own, rotate the antenna only to the vertical position and not to the stop position. Part of the key will be behind the flange so that the antenna will not come off. Under no circumstances should you use a tool to pry off the antenna. This will snap off the plastic so the antenna will not be held in place. You will then have to use an external antenna for a reliable connection.