This is the situation:

around the pond, i purposedly am leaving about 5 extra feet of over lap:

i want to dig an 18" escavation all around the entire circumfrance of the pond which is 12"-30" wide [depending where] and place a liner in the escavation; i want to fill it with a substrate that will allow for ferns, pickerel plant, marsh-marigolds, iris, arrum, cardinal plants, etc. to grow, some of which will not thrive in an acidic peat filled bog-garden.

What should i use, if not soil and peat?

If i use soil, what if one side of the escavation received a liner all the way up to ground level AND the opposite/parallel side only gets the liner to go up part, most, or nearly all of the way, so that there will never be standing water and there will be constant moisture dissapation into the surrounding soil?

in this way, can i use soil? ultimately, im going to end up trying it and seeing if i can form a ballanced solution that will: maintain sufficient moisture and fascilliatate sufficient drainage so that these marginals will have enough moisture to thrive and there wont be an extremely high rate of decomposition.

let me know what you think?