You DO NOT want to "just walk around the fence" (unless you were just talking about walking around outside the fence). The boneyard is part of Davis Monthan AFB and those planes are still considered combat ready and it is guarded by armed AF mil police. If you are out there and are not authorized to be they will arrest you...probably not the day you would want. If you are a military aviation fan you might also want to check out the Pima air and space musuem just around the corner.