not an arborist but am a forester - emerald ash borer for you guys in the states is a clear worry- i hope you dont swap with us and get chalara.

pine trees on the hole are a safer bet- but be aware of hanging in areas near where felling has been done as trees are now exposed that were once protected and thus not setup for high winds.
as others have said always look up and unless your unlucky always setup early so you can see the canopy around you - not just your trees but for a sensible distance around you - as hung up trees can fall at any time and be up to 60 feet away//

on other signs - look for fungi/brackets on the stems of hardwoods and other already dropped branch debris as clear signs that the tree may not be well. same with any cracks or oozing cankers splits.

many people forget that trees have shallow roots and are not like a childs drawing where the roots are deep - usually they are not much deeper than 1m / 3ft but spread as much as 2x the canopy width.