Question
  We have three leyand cypress trees in our back yard .  Our neighbor wants them topped because they are shadding her swimming pool. What would you recommend.

Answer
Topping is the practice of removing major portions of a large tree's crown by cutting branches to stubs or to the trunk. Some homeowners think their tree is too big and therefore, unsafe; some believe it is good for the health of the tree; some simply planted the wrong tree in the wrong place (under utility lines, for example) and need to "whack" it back into its space. Tree topping shortens the life of your tree, creates weakly attached limbs prone to breakage and disfigures your tree.

It all depends on the size and it sounds like these are now large trees. Leland cypress can be sucessfully topped when they a young but will look like hedges not trees. In older trees the tree will not recover and may start to die.

So I would say NO to a neighbor that wanted me to top my trees. A compromise would be the neighbor pay to take the trees down and replace them with smaller lelands that can be pruned and shaped to keep them from shading the pool.