Personally I ditch out a good distance from all structures and even include a copper node or two if I can.

If you can't ditch due to water then I would consider moving my location so I could. Hillsides are good since you can just carve in a drop off rather than a ditch.

Not a fan of building by water... takes a lot more effort to make secure base defenses.

Edit add - The ideal situation in that regard for me would be to find a copper node as close as possible to iron crypts.