All of a sudden start to notice large bees hovering around your fence? This time a year they are most likely carpenter bees. Think of them as a mom and dad bee, mom takes care of the not yet born young and dad hovers outside of the hole the bee lives in and protects his family. Funny thing is the dad bee doesn't sting, the mom does. What the dad will do is intimidate the heck out of you. Go near the area the carpenter bees are living and you will get chased.
How do you get rid of them? Always use caution. There are pest control supply products you can buy online. The treatment is long and tedious. There are often times many many holes. The other option is hire a pro. The last and most expensive is to simple replace that wooden fence or structure with a plastic fence. I think I soon will be getting a plastic fence. I hate these bees!