No, your neighbor cannot attach anything to your side of a garden fence. If you give permission, they can. Contact your zoning inspector or city attorney for your specific laws.
If the neighbor has agreed to help pay for the fence and failed to follow through, then you could go to small claims court. If the neighbor does not want to help pay for a shared fence, then your choice is to go it alone or not to build the fence at all. You cannot force a neighbor to put up a fence.
No, you cannot. The fence is the property of your neighbor and you have no right to paint it.
can my neighbor (in California) use by fence as his, the fence is on my property
(If you can prove that it is more likely than not that the neighbor dumped the fence panels): Hire a licensed contractor to remove the fence panels. Then, take the offending neighbor to small claims court for the amount of money you paid the contractor to remove the panels.
It is not possible to attach to a neighbor's fence unless permission is given by the neighbor. It is a good idea to get any agreement in writing for attaching to the fence.
does the fence separate your properties?
No, you have no right to attach a fence to your neighbor's fence unless you have her written permission.
If the grapevine is growing onto your property, you can trim that growth back, but you cannot destroy anything that is on your neighbor's side of the fence. You must also offer your neighbour the prunings back as they belong to him/her.
My neighbor would like to remove the fence that we share in our backyard. Is he allowed to remove the neighboring fence without my approval?
If the fence is yours - ie your boundary and on your land then the neighbor has no right to attach anything to it (without your permission).