If that is the only way to his property for the line, it might be a valid easement.Listen to your local lawyer, but the easiest route may be to make an official, recorded easement of what is than to fight it. 

Kind of like if a cop gives you a speeding ticket, the cop shouldn't also get to be the judge if you choose to fight it, right? 

His craigslist/hotpads/zillow/trulia b/c your tenants will look at them and see if they can find a place and use that to fight your case. 

What can I do to fight the increased assessment?

If so, here's how you can fight...Demand that real estate agents and, especially, brokerages you hire do not syndicate your properties to third-party sites like Trulia and Zillow.

from my point of view if your an individual and not partnering with folks who ever is going to sue you is going to name you personally.. this is where you need good insurance to take up your defense as your first line of defense.whether they have the right to sue you is immaterial.. or whether they will prevail is immaterial.. if your operating as a group or partnership and have clean records this can limit your exposure to your ownership.other than that  retirement accounts should be maxed out they basically cant be touched... certain trusts.but just LLC labyrinths like you mention.. those are not going to do it for most or.. you will spend a ton of dough fighting to make the position they can't sue you. when suits happen everyone is named .. that's when you need good insurance to handle your defense.

Some areas really don't like the scrap-and-build-giant-triplex approach and will fight you.

I'm not going to fight her over it, I can get somebody moved in easily but I am more curious for my own knowledge since this is new to me.

Landlords try to fight us at 1st they do the whole "i'm not paying for a tenants gas" yaddda yaddda.

If I had 8 sub-100k listings and was having to fight with my seller on every one to get them closed without him messing them up, I may start ignoring people too...haha.