If you are very careful and do not have plants close to the pathway I have used Roundup spray on my daughters gravel paths and borders and it has always been successful. But do not do the spraying on a windy day as the spray will travel in the wind and kill other plants it lands on.

Pathclear or Groundclear, BUT Groundclear shouldn't be used if there is planting very close to the path. Pathclear will keep weeds at bay for around 3 to 4 months, and should be applied either by sprayer, or a watering can with a very fine rose to reduce the risk of run off onto nearby plants.

Roundup and the like are contact herbicides and don't have a residual effect.

Elbow grease and perseverance l have always worked for me