If you lay the gravel properly, (i.e. get it rolled when it's first laid), and give it a bit of cursory maintenance (raking it once a week), it should last a lo

If you lay the gravel properly, (i.e. get it rolled when it's first laid), and give it a bit of cursory maintenance (raking it once a week), it should last a long time without you needing to add any more gravel, or at most adding a bag of gravel once a year.