The diversion ditch will probably do wonders for you, small pond. Maybe even a couple of them. You might also consider just randomly placing rocks around the hillside above the pond as a means of slowing down any water that gets beyond your ditch(es), kind of like creating a space where there is no single straight path to the pond, forcing the water to basically ricochet down the hillside.

Todd La Neve

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1.5 & .5 ac ponds - LMB, BG, RES, YP, GC, HSB