Without more information this question is too broad and open-ended. You haven't even specified how the aliens control the minds of humans. How should we tell you how to defend against the unknown?

I haven't gone into detail, but they can by showing certain images, emitting certain sounds, sending chemicals to the air that can be breathed, some chemicals that if ingested would produce the effect and substances that if touched would produce the effect. As a beginning I think it's enough detail.

My point of defense is about killing them, so I guess I should specify it.

Is there a reason you can't just snipe them from a kilometer away before they see you?

Now this is becomming quite an interesting question, but it's still a little too broad. If the aliens control minds by pheromones, you could plug your nose and shoot them down. If they somehow control anyone who sees them, it's a completely different situation. I propose you choose one way of mind control (visually, acoustically or chemically) and concentrate on that. If you're not happy with the answers, you can later ask a new question concentrating on a different way of mind control.

Do they infiltrate singly? If not, I'd blow up the entire area they're known to be in. And if they've infiltrated singly, you've already lost.

@John Locke, as far as I know a ship horn can be heard from kilometers away, even if he were to have ear protection I doubt he wouldn't listen anything, also there's a risk of them showing the mind control image, via a huge hologram, and in any case if they are in group and one of them is killed but some of them are alivee, they'd automatically try to use any mind control method at the biggest scale they could, which would likely result in greater loss for humans.

@user2638180 I said snipe, as in shooting them from a distance with a gun, so I don't know what ship horns have to do with this. What if you used an attack drone with radar instead of a camera, so they couldn't show you the image? You would be far enough away to avoid pheromones or sounds.

@John Locke, what I meant is that if you prepare an ambush with snipers, but one of the aliens make that mind controlling sound before with a good equipment before being shooted, one that would be as loud as ship horn, which looks like that could be heard from a higher distance than a train horn and that's already 8 km (quora.com/…), would automatically leave them mind controlled even if they were to have ear protection.

Some other points of clarification: can the mind control be fought in any way or is it absolute? Do the aliens need to be aware of humans to control them, or is it automatic? And can they control other animals, or just humans?

There are an infinite number of ways to kill anything. For these aliens, literally anything automated would get the job done, even a roomba with a kitchen knife. I feel you need to add in some more info, such as tech level availale, to get any meaningful answer.

@user2638180 Sound is distorted over large distances, so the effect of mind control could maybe work less efficient...

Ok, now I understand what you meant by ship horn. Would the drone idea I mentioned work? If it will, I will post it as an answer and try to elaborate a little more.

I just realized you haven't provided any detail about the humans' tech level. Should we assume present day/near future technology, or something more primitive? This will be important to give us options to kill them with.

@John Locke, I edited to put present, whatever we have at our disposal right now. Yes the drone idea seems nice, but even if we get to spy them I doubt if we have enough resources to make something wander searching them and identifying them properly.

Yes, guess it would be valid, as long as the drone can recognize them, which I don't think would be easy but maybe we have enough tech for that, apart from that, point is if we have enough resources in order to keep lots of drones wandering.

How many aliens are there? 10? 100? a million? You also said they are invading earth, but if they are aliens, how did they get here with stone-age weapons? I would think weapons would advance along with rocket technology.

Millions of them are to invade but they are doing it strategically as seen in my comment for Ister answer, they never bothered into developing weapons for destruction as in their home planet most of their creatures were basically inmune to physical damage, a dynamite cardtridge would be needed to slightly hurt the weakest of that creatures, but discovered that could control them by certain odors, certain food, etc, when they finally decided to conquer outside space they were into using what they had been doing for lots of millenia, they didn't even consider destruction weapons.

For this question to be answerable we, at the very least, need to understand how the mind control process works. What is the mechanism, what is the range? It also appears that your question is not "How do I defend against mind control" but "How do I safely kill aliens with the ability to mind control someone" It would also help if we understood what your desired end state is...if you don't mind nuclear wastelands...well then...if on the other hand you want as little destruction as possible... Additionally we need to know the scope of the invasion and the invaders' methods.