Fortunately, we don't have this problem with our dog. But I have friends that do and they use the plexiglass idea as well.
2013 Jayco Eagle 328 RLTS
2013 Ford F350 6.7L 4x4 CCLB W/Air Lift air bags
2002 Coleman Bayside Elite (traded)
Me, Momma and Charles (RIP buddy)
And introducing Sofie!! ;)