Comment 78 for bug 1205384

In order to make xfce4-power-manager support lxlock for locking in general case, you could add certain symbolic link to it:

sudo ln -s -T /usr/bin/lxlock /usr/local/bin/xflock4

This would make Xfce also use lxlock as its locker, if Xfce is installed in the same system. Please test.