As you know, sometimes you have a choice as to which way the debris goes. If possible situate yourself so that the trimmer is slinging the debris away from things that can be damaged by it.
I know this is as simple as it gets, but sometimes people are in too big of a hurry and don't slow down and think about even the simplest of things.
Shut 'er down Buford....she's slangin' oil !!!!