Here's what I would do...
I would go over there in the early spring before you start improving anything and strike up a conversation about the hunting issues. Don't do it now.. do it in the spring when there's "no hive to protect" and no one feels the need to sting.

Tell them you are going to be making some (yet to be determined) improvements to your land and that you think it would be a good idea if you two got together to come up with a plan so you don't interfere with each other. (bring a map of your properties and some magic markers so there's no misunderstandings)
Also make sure to inquire and confirm his control over his guest hunters.

This good faith offer and consideration now gives you a window to politely voice your complaints in a nonchalant way that won't put them in a defensive position.

In short, you are going to pretend to accommodate them in an attempt to draft them into your circle of influence.

Worst case scenario, you have to post your property to keep them off and do the best you can with the land you have to work with..
If a neighbor is intent on being a jerk, there isn't much you can do about it except defend yourself.

Best case scenario, you both come up with a plan and you both improve the entire area so much that it brings in more deer than either of you need.

That is a bad idea as an opening move..

If you are forced to declare all out war, then you can implement this type of thinking. But not until you've exhausted all other options.

I agree with Murby that you should have a civil discussion after the season and before the next season. I do agree that " no trespassing" signs along with good boundry stakes will also help your position. If you are mad/pee-od when you go to see them it will not help and only hurt your position.

CVG Ohio

No matter what you do, these neighbors will find a way to mess it up as soon as they hear you shoot should you find a way to successfully gun hunt. About the only thing you can do is bow hunt in a way that they do not know where you are. And forget about the gun hunt unless it is someplace else. And never let them or any of their friends know if you got a deer.

You might seriously consider moving or saving up to buy a nice chunk of land.

I can totally relate, believe me.

Check out any hunter harrasment laws in your state. Then if they drive that ATV around your stand with you in it you can have them charged fof that also. Let them see you making a video with you in the stand. Do everything legally and above board and you will eventually make your point.

I had some hunters trying to cut deer off from me once. I just kept shooting the deer they were running to me.

" And never let them or any of their friends know if you got a deer." MZS, I can't agree more with this. We have mutual friends with the people that hunt to the south of us. We no longer send them pictures or mention our deer to them. It seems that in recent years with the popularity in texting has hurt our hunting because they've seen all the nice deer we've got and now try to cut us off. Our hunting hasn't been as good in the last few years. A buddy took a pic of a large buck I shot and texted everybody and their brother about it. I had people facebooking me and approaching me in publics about the deer. It was irritating because we don't publicize our success.

I don't get it.. Are you afraid they're going to sneak into your freezer and steal it?

Tampering with a survey marker is illegal. Report it.
As far as their shenanigans on their own land. Nothing you can do about that.

Murby, I'm not worried about the larceny of our venison haha. I'm just thinking that if they don't know about what we've got then it may lessen their attempt at cutting us off and focusing on other parts of their land. This may sound a bit paranoid, but with the popularity of social media, we also fear that the wrong people may see these photos and trespass/poach on our property. We only feel this way because this it was a big issue several years ago. We blocked off some of the ways people were accessing our land and it eventually stopped.