Any suggestions on controlling runaway mulch in the high desert of N. California?

Working on a private residence off of highway 5 about one hour south of the Oregon border. Very windy in this area and when it rains it pours! "Man it pours".... There are rocks edging most of the beds, however this particular area is without rock and there is a slight slope with mulch. It seems if we edge the area with rocks it may take care of the runaway mulch. After a heavy downpour the driveway is littered with mulch. This bed that is not edged is next to her driveway. Any suggestions would be appreciated! May post pics later from my phone.