If you’re thinking that dense development would be really upsetting to you in the long term, or would significantly devalue your property, the time to sell is now, before the developer has filed plans that become public. It’s up to the new buyer to do their own research on the county master plan, find out who owns the surrounding properties, etc.
Or if you want to stay put, I agree with investing in thick screening plantings and thorny bush barriers now. I would not wait for the developer to pay for it, unless they’re asking for a rezoning or variance, which would give you a little more leverage to make such demands.
But in general, if you want to control what happens on the land all around you: Buy. More. Land.
Sorry, but it just bothers me when people buy properties that are too small to insulate them from the activities of their neighbors, or buy land where there are no zoning laws, and then get outraged when these decisions come home to roost. I have no problem with demanding that development be done in a way that does not infringe on your property rights (such as water rights, setbacks, etc). But as long as a neighbor is conforming to the zoning rules (and/or they follow the legal process to adjust those zoning rules, which gives you and others the right to provide comments in opposition), they have the right to use their property as they see fit. Just as you have the right to put your horses right up near their property line (even though your new neighbors may view them as stinky, dangerous farm animals that attract disease-carrying flies).