You can keep your gravel path free of overgrowth and the like by using weed barriers that gardeners use to keep the lawn out of their flower beds. This stripping can be bought in various widths and depths, and generally comes in strips or a roll for easy handling and installation.
Step 1 - Lay out the Weed Barrier Sheeting
If you have a gravel path in place already, take your shovel and split the path in half, moving all the rock to the other side, so that half of the path is clear of rock and debris. This would include pulling any weeds that have started to grow up through the middle and sides of the path you are working on. Try and remove them all the way down to the roots if possible, to prevent them from possibly surviving and undoing your work down the road. Take the weed barrier sheeting and lay it out over the cleared area, folded in half length wise up the trail, this is going to lay under your rock bed, preventing weeds from growing up through the middle of it.
Step 2 - Trench the Path for the Weed Barrier Strips
Once the gravel path is clear on one side and you have the sheeting laying in place, use your shovel or spade to dig a trench along that side of the path all along its edge. Once the trench is dug, tuck the edge of your sheeting in there and place your barrier strip over it, running all along the side of the path. So one side of the path should have a weed sheet barrier running into the edge of the trench on one side, with the weed rail sitting on top of this. You can cut the stripping and sheets as needed with the utility shears.
Step 3 - Form up the Sides of the Path
Start on the side you have trenched and covered along the gravel path and form the edges of it together. To do this, add dirt that has been dug out during the trenching to the outside of the stripping to stabilize the rail from moving or falling over. Then move all of the gravel from the other side of the trail to the sheeted side. Be sure to fill the gravel in closest to the edge of the path, keeping the sheeting flat and even as you go. Once all the gravel is on the other side of the path, you will want to repeat the steps on the other side as well. Dig your trench and lay the weed sheet flat into the trench, and insert the weed barrier.
Step 4 - Level out the Gravel Bed
Now you should have a weed barrier running along the side of your gravel path on each side, and then under the path gravel itself a weed sheet to help prevent growth up through the rock. Level this out evenly and be sure that the edges are packed tightly with gravel and soil to ensure that water does not pool up on its edges, in rainy weather.