Hammer wooden stakes in the ground with a rubber mallet and wrap a string line around them to outline the border of the path. Dig out the sod with a square-edge spade by piercing the outline under the string. Cut the sod into pieces with the spade and pull it up by hand.
Dig 4-inches of dirt from the trench and check the depth periodically with a tape measure. Get the edge lines vertically straight and smooth the bottom with the edge of the spade to get it mostly level. Tap the bottom soil down with a piece of 4-by-4 scrap lumber to compact the soil.
Shovel a base of crushed stone into the trench to a point 1 1/2 inches from the surface. Smooth the crushed stone with the back of a metal rake to get it even across the bottom. Check the stone surface with a 2-foot level and fill low areas or rake high areas.
Spray the crushed stone lightly with a garden hose just enough to moisten it. Tap the stone with the 4-by-4 piece to compact it firmly.
Position galvanized metal edging against the side of the trench. Place a 16-inch piece of 2-by-4 lumber flat on the crushed stone base and against the edging so that the metal is positioned between the wood and trench edge. Hold the wood in place with your foot and place a 6-inch block of wood over the top edge of the metal and hammer the wood to force the metal down so that the edging is even with the top of the sod layer. Move the blocks as you hammer the entire edging in place.
Lay landscape fabric over the top of the crushed stone base and cut it to fit the width of the trench with a utility knife. Overlap any joined pieces by 4-inches to insure a good seal between pieces.
Pour gravel into the trench and rake it evenly over the surface of the fabric. Fill the trench to 1-inch below the top of the metal edging and walk the surface a few times to compact it in place.