We have all encountered this.  Part of the fencing is leaning or falling down.  The fence is old and needs to be replaced.  Who is legally responsible for paying for that fence?  As it turns out the cost of repairing or replacing that fence is legally shared between the affected owners.  What I was unaware of was that written notice describing the needed repairs, cost of repairs and description of repairs needs to be given to the adjoining landowner.  And 30 days notice is required.  If the next door neighbor is a renter the legal owner needs to be found and repairs agreed upon.  For more information on the legalities of this issue go to http://law.onecle.com/california/civil/841.html.