What slows erosion?

Answer 1

Erosion can be slowed in a number of ways, but by far the cheapest is to plant vegetation. After that, it would depend on the type of erosion you are trying to slow down...

Marine erosion

To slow down Marine (Sea/Ocean) erosion, you could build an artificial reef, dump sand and/or various debris on the shore (which would be potentially unsightly) or you could build a sea defence system; including a sea wall as a secondary defence, and with wave breaks as a primary defence.

Fluvial erosion

Although there are small scale erosions like rill and gulley, these are very difficult to source and eliminate. A river, however, can be far more devastating, and also far more easy to track. A river meander (bend) is a fickle landform, and moves with exceptional speed (in geological terms). One can move from one side of the valley to another in decades, and can disappear completely in the same time. To prevent the movement of these meanders, farmers reinforce the outside bank of the meander with concrete or with metal rods.

Aeolian erosion

There's really not a lot you can do here: apart from planting vegetation, there is little protection from the wind.

Glacial erosion

Glaciers are unstoppable. Unless you used some kind of a huge flame-thrower etc. you could never hope to stop a glacier. On the other hand, glaciers aren't worth worrying about as the only rocks they erode are those they are in contact with, and that's not rock that you'd be worrying about - unless you reside somehow on the sides of the trough...