Landscaper Job in Denver, Colorado

Hi, there is small; maybe 6x12 area within my fence that Id like to transform into a flower garden. There will need to be some sort of barrier to keep the dirt in between the fence and so that dirt doesnt spill out on sidewalk and so that when fence is replaced there wont be issues with the dirt/garden. Currently theres rocks on top of dirt. Id like to get rid of the rocks, add dirt deep enough to plant flowers. Ill put fake grass on top as nobody has time to mow!