rock retaining-wall (old) -- big holes -- how to fix?

Our driveway is sunk maybe 5 feet down from the level of the front yard, and they're separated by a rock retaining wall. (Rocks maybe 5 to 10 or 12 inches wide/high, don't know how thick (going back perpendicular to the wall.)
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.))
Ideas welcome!
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?
Thanks!
David
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On 15 Jul 2008 13:19:58 -0400, snipped-for-privacy@panix.com (David Combs) wrote:

Just something to keep in mind: Not that I've ever built one, but I see a lot of tipped over retaining walls. I think is due to water pressure. IMO, you need good drainage from the back side. One way to do this is to leave the joints fairly open.
G
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the easiest best long term solution is remove wall completely and regrade yard, plant groundcover on slope.
no wall means this will never happen again.
retaining walls fail way too often. and few want to spend the bucks on a real solution.
with a proper footer, below frost line and all the rest to do a good long term job
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