In Lancaster County, a 12-year-old boy died Sunday morning after a tree holding up part of a zip line broke and fell on the child. To prevent tragedies like this, local arborists are sharing how to ensure trees are safe. Certified arborists, like Carl McDonald with Bartlett Tree Experts in Mountville, said the sturdy trees, such as oak, maple, or hickory, are best for tension activities. Still, McDonald said the health of the tree is what matters most. He said that an unhealthy tree can sometimes be obvious."Even before somebody like me comes out to inspect the tree, you know, make a good choice," McDonald said. "Look around, make sure nothing is going to break off."Other times, McDonald said it takes a professional to find the liability lurking among limbs. "I would probably look at the base of the tree, make sure there's a nice root flare, make sure nothing is constricting the flow of nutrients and water up and down the tree," McDonald said. "Secondly, I would look up at the top of the tree to make sure there are no defects, broken limbs, or dead limbs that could be shaken out. You want to look for cavities and other types of defects that could occur in a tree."Though McDonald said arborists are willing to inspect trees for residential zip lines, they'll never recommend them and say no matter how healthy a tree is, there's always a risk.