yeah the county may help due to the erosion IF it poses a potential danger so sure call them. You can suggest anything you want to the neighbor including separate fences or mt suggestion is you can offer to credit the amount if the cheaper one toward the stronger one and you pay the difference. He may physically be able to tear it down and rebuild cheaper one just like you can do the same but you can not force him to pay half the expensive one, (absent county requirement).So you take charge here and build what you want with his written agreement and have him pay you first toward better fence. The tear down is shared cost
The foregoing is for informational purposes only and may not be relied on as attorney-client advice.
California "good neighbor" fence law used to be relatively simple: neighbors had to share in the reasonable cost of erecting fences. The California legislature, in its infinite wisdom, has recently enacted a complex procedure for resolving fence disputes that unfortunately requires the involvement of an attorney in many cases. Whether or not they can erect a fence without your agreement depends on whether or not they've complied with the new statutory procedure.
It may still be possible to work something out with your neighbor. If you want a nicer fence than your neighbors, consider trying to negotiate with them so that you still split the cost, but perhaps you pay a slightly higher percentage. That would certainly be less expensive for both parties than erecting separate fences, and you could still get the fence you want.
You may wish to speak to a local property attorney or an inexpensive neighborhood mediator to determine if there are some low-cost options to assisting you and your neighbor resolve this issue.
ATTORNEY ADVERTISEMENT. Of course, without having heard the whole story and reviewed the relevant documents, I can't give you advice, just my general opinion. If you're serious, you should contact a local attorney, rather than relying on any opining on the Internet. Jason L. Eliaser is licensed to practice law in California (State Bar number 248394.) This is a communication concerning my availability for professional employment within the meaning of California Rule of Professional Conduct 1-400(A). Viewing of this post does not constitute the provision of legal advice and no attorney-client relationship is formed by viewing or responding to this post.