If you walk to the right place and stand there:
(google maps)
https://maps.app.goo.gl/y1xpUTwDfszBP4Fi9
...all you have to do is hold your thumb up.
Many people driving out the back gate are already going to Rose Barracks anyways.
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It's safe there for drivers to stop on the right side and pick you up.
If you think having a permanent Ride Share location at the back gate is a good idea, say so in a positive ICE comment to DPW.