Legal Question in Real Estate Law in California

To the extent the fence is the neighbor's and remains on his property, there's not much you can do about it. The possibilities are pretty much limited to studying up on, and then trying to enforce, any local laws, ordinances, rules, etc, (zoning, neighborhood appearance, HOA, or something of this kind). You won't find any in many neighborhoods, but elsewhere there may be such guidelines in place to protect property appearance and values. In a very extreme situation, you might win a private-nuisance lawsuit. Maybe take some pictures and then get an opinion on this from a local real-estate or land-use attorney.

However, to the extent the fence actually leans across the property line, it is a trespass. You would then have a limited right of self-help to abate the trespass, meaning you could, for example, drive some posts or stakes to prop it up and away from your property. You could also sue for trespass. The problem is that small claims probably has no jurisdiction to order abatement of a trespass; it is pretty much limited to money damages (and then only up to $7,500) and it's doubtful you can prove monetary harm; going to superior court could be costly and time-consuming.

Finally, you should look at Civil Code section 841, subsection (2), which says "coterminous owners are mutually bound equally to maintain ....... (2) the fences between them, unless one of them chooses to let his land lie without fencing; in which case if he afterwards incloses it, he must refund to the other a just proportion of the value, at that time, of any division fence made by the latter." Courts have held that, under this law, a property owner becomes liable for half the cost of maintaing a boundary fence if and when he "encloses" his land entirely. If your neighbor has entirely enclosed his land, i.e., because he has a dog that he doesn't want to get loose, then section 841(2) kicks in, and he has to share the maintenance costs of a boundary fence. In such a situation, I'd say it would be a boundary fence even if it were entirely on the neighbor's side of the property line, if it is functionally a boundary fence.