Posted: 22/07/2015 at 21:13
You don't want too much soil ending up in the pond as it contains a lot of nutrients which encourages algal growth. Is it a wildlife pond Pam? If so, normally you would have a slope, or beached edge, of gravel so that creatures can get in and out safely. The gravel then blends into the planting areas and soil doesn't really get washed in much because of the gradient.
If you just have an edging of rocks etc, you can use a strip of landscape fabric as a barrier between your planted areas and the rocks which will prevent the soil slipping in. The plants will cover it or you can use some smaller rocks and stones to disguise it.
I created a small pond last year. The first pic shows the little barrier I have between the planting area and the little pool which now has some marginals. I used some heavy duty plastic over a few rocks :
This is the same area planted up and top dressed with gravel to hide any bits of plastic etc :
The plants are all quite mature now