Anyway, over the years the water pressure (rain) has, in some places, washed out the concrete or grout or whatever they used for binding it all together.
So they're holes between some of the rocks, of size, at the largest, maybe six inches in both directions.
Question: what to do about it?
And how much work might it be?
(Something you do yourself, or instead hire someone? (Here in Westchester County, NY, just north of the Bronx, there's lots of (mexican, central-american) immigrants who seem to know rock-work.))
Oh, whatever you use to fill up the holes, do you have to make a big deal of mixing it, or might it come "ready to use"? Pros and cons?