Norm, maybe try poisoning just one of the trees - often as the conifer/cypress gets weak, it gets that canker stuff, which can easily be transmitted to adjacent trees and naturally kill them as well.
My Grandmother originally planted one about 4 metres away from the house (not the smartest idea) which constantly filled the gutters. It died, and now there is a shed where it was. Then there were 2 down the back corners a few metres from the fence which both died, 1 in the middle of the yard which was on its way out, another to the side which spontaneously dropped dead.
The last one fell in a thunder storm in the most perfect way - missed the house, shed, fence and power lines
The photo is the last one we cut down, partly because it was on its way out, but mostly because it meant our neighbour wouldn't be continually cleaning up all the conifer litter in his yard and he is a great neighbor
