Advice regarding the neighbors fence

[Carrie Giordano]

I just finished rehabbing a rental and need some advice about a fence. The neighbor has a double lot which puts their backyard next to my front yard. Her yard is enclosed with a very old, metal wire fence (looks like a farm fence.) Not only is it an eyesore but her dog seems to want to attack everyone who pulls in my driveway, which is on the same side as her fence. She swears the dog is nice and it's the old owners fault for being mean to him! I know this dog will be an issue for potential tenants so I am planning to extend a privacy fence as far as the city will allow me. This would basically be a 6ft shadowbox fence until the end of my house and then a 4ft fence for another 12 ft. I spoke with the neighbor about replacing her fence. At first she seemed opposed but then seemed to like the idea of more privacy. She agreed to let me replace the 44ft of her fence with mine if I could secure her fence to it so that her dog cannot escape. My question is, I know I need to get this in writing but am unsure of how to protect myself without scaring her off? She is very defensive of the dog and kind of seems like she could change her mind about the fence and be trouble. Any suggestions on what needs to be written without being overly formal?