Retaining walls do not fall over without warning. They lean for a season or two first, and almost everybody who calls us in an emergency had noticed something months earlier and hoped it would settle.
Walk the length of yours after a heavy week of rain, which is when everything shows, and look for these.
It is leaning
Hold a level against the face. A properly built wall leans slightly back into the slope, a degree or two, on purpose. If it leans out toward you at all, water is getting behind it and pushing.
This is the one to act on. A wall that leans out is not going to correct itself.
The top course has moved forward
Sight along the top from one end. If the top row has crept out ahead of the row below it, the wall is failing from the top down, which is usually the cheapest failure to fix and the most reliable early warning.
Soil is washing out at the base
Look at the ground in front of the wall after rain. Fans of sand or silt on the grass mean water is running through the wall rather than draining behind it. The drain line is either blocked, crushed, or was never installed.
That last possibility is more common than it should be. We have opened plenty of walls with no gravel and no pipe behind them at all.
Cracks that run through blocks rather than between them
A crack following a joint is usually cosmetic. A crack running straight through the face of a block means the wall is carrying load it was not designed for, and something structural is happening.
Vertical cracks near the ends of a long wall are worth particular attention.
The ground behind it has sunk
A dip or a trough in the soil directly behind the wall means material has washed down and out. The wall is quietly losing the backfill that holds it in position, and the dip will get worse each storm season.
What repair actually involves
For a wall under about three feet with a top course that has crept, we often take the top two rows off, correct the base, and reset them. That is a one day job.
Anything leaning outward through its full height gets taken down and rebuilt with proper drainage. There is no partial fix for that, and anybody offering you one is selling you two years.
Walls over four feet need an engineer before anybody touches them, which is county rule and also common sense, because at that height the wall is holding back several tons of wet Florida sand.