@REI-LizH I have a  Border Collie who loves to run (and chase balls, squirrels, frisbees - loves life). The hard part mountain biking with her is she does not stop.  She will now drink out of CamelBak when I squeeze the end, so water is vital and not too hot or too long.  When I take her on bike path I tow an old Burley, so runs a bit and rides a bit.  I did this with my previous dog and as we rode past a family the young girl, observing my dog in the trailer, turned to her mother and said. "You know, you can put babies in there."  I believed my dog and I blushed