Frequent inspections, perimeter spray all units, and treat each occurrence asap.

We just had a medium sized rainstorm and when I went out to the garage I noticed water leaking at least two feet inside the entire perimeter of the garage (only about 1/4" deep). 

Professionals drill (two feet or the longest masonry bit available) into the hole every 24 inches around the exterior and interior (if the basement is not finished) perimeter of the building and spray the chemical into the hole.After you have sprayed the chemical in the hole patch the hole with cement so the rain doesn't flush the chemical out.

Most of the Duplexes and Quadruplexes are in the city or in the perimeter.

I agree with a couple of things already mentioned: DIY or hire someone to do regular perimeter spray in each unit quarterly.

I cannot attest to its longevity but it is advertised as waterproof (although extra steps are needed at the perimeter if installed in bathroom/kitchen where water could be a problem).

StoutStout Kaiser Matteson Peak & Hendrick1117 Perimeter Center WestSuite W400Atlanta, Georgia, 30338 

So far I have only one contractor bid for perimeter foundation for 70k but with only 1 year warranty which makes me nervous.

We're looking at neighborhoods that are already in good shape, or are pretty close to getting there... west of 75/85, but inside the perimeter, from Grant Park north to Morningside/Lenox Park.

The similar comps that are 1/2 mile away could be used as well, since that is within a good perimeter as long as that doesn't end up being a different neighborhood or cross a major artery.