Step 1
Open a bucket of roofing tar and put on gloves.
Step 2
Dip a wide bristle paintbrush into the roofing tar so three-quarters of the bristles are coated. Let the excess drip off.
Step 3
Paint the fence posts so they're thoroughly covered in the roofing tar. Use the end of the paintbrush to work tar into any of the groove or indentations in the fence posts. You need a thorough coating to keep insects and rot out of the posts. Don't worry if the tar looks uneven, it serves a functional, not aesthetic, purpose.
Step 4
Continue painting the fence posts until they're all covered. The roofing tar will take 12 to 24 hours to cure, depending on the weather conditions, such as humidity.