While such wording wouldn't hurt, I doubt you'd ever need it.

There is also law concerning the duty people have when doing each other "favours".

For example, if I ask to borrow your car to drive my date to the Prom, I have a much higher duty to look after your car to make sure no harm comes to it than if the situation were reversed and the benefit of my having possession of your car was to you.

If you came to me and asked me to allow you to park your car on my property for a few days until they finished paving the street in front of your house where you normally park, then the benefit of my doing that favour is to you. Or, if you asked me to use your car to drive your mother to the supermarket to do her weekly grocery shopping, then the benefit of that favour goes to you. In that case, I have a much lower responsibility to ensure that no damage is done to the car while it's in my possession. If someone comes along and spray paints your car while it's parked in front of my house, then you can't sue me for failing to take reasonable care to protect your car while it was in my possession, such as parking it in my garage.

That is, when you ask someone to do YOU a favour, then the onus is on you to find someone who you trust is responsible enough, or has sufficient resources (like a garage large enough to accomodate yet one more car) that you feel confident entrusting your car to.

It's the same thing with allowing someone to use your land. If you allow them to grow something on your land, then the benefit of that favour is to them since they will harvest whatever is grown. They have a much higher responsibility to take care of your land (and ensure that no harm comes to it (such as someone dumping toxic waste onto it), or harm comes to you as a result of granting that permission. If the situation were reversed, and you were sick and asked them to farm your land for you, then the benefit of them doing you that favour goes to you, and they have a much lower responsibility to ensure no harm comes to your land as a result of them farming it for you.

If I recall correctly, if the benefit of someone doing you a favour is to you, then that other person need not exercise any higher level of responsibility "than he has". Which means that it's up to you to pick a RESPONSIBLE person to ask a favour of. If the person you ask to do you a favour is irresponsible, you have no one to blame for the harm that comes to your property than yourself.

So, in a case like the one you cited, no judge would hold you partially responsible if you allowed your neighbor onto your land to grow flowers, or whatever, and their hired help injured themselves while working on your land. The benefit of the favour is to your neighbor, and it's his responsibility to ensure that no harm comes to you, or your land, as a result of you're doing him that favour.

So far as I know, the only exception occurs when you're aware of a hazard on your land that the Neighbor isn't aware of, such as a tree root or rock sticking up out of the ground that someone could trip on or a low hanging branch of a tree that someone could hit their head or, perhaps conceivably, poke their eye out on a secondary or tertiary branch of that low hanging branch.

So, while having something in writing absolving you of all responsibility for whatever happens on that land wouldn't do any harm, it almost certainly wouldn't be needed since the benefit of you're allowing your neighbor to use your land is to him, and not to you, and every judge would recognize that.

Few, if any, judges are mentally retarded, and every one of them would recognize that your letting your neighbor use your land is a benefit to him, and therefore he has the responsibility to ensure that no harm comes to you or your land by granting him permission to use your land.

If the Mexican fell and cut his hand off on your property, the onus would be on the Mexican or your neighbor to prove that you were aware of a hazard on your land that you failed to reveal to the neighbor, such as a rock or tree root sticking out of the ground. If tree roots grow without your knowledge (Duh!) then there is no way the Neighbor or the Mexican can prove that you were aware of the hazard at the time you gave permission to use your land to your Neighbor. In that case, you can't be held responsible for the Mexican cutting off his hand since you were unaware of any hazards that could come about in future when you gave your permission to use your land.

This is entirely why the addage "Lack of knowledge of the law is no defense" rings true.
As long as you act in a responsible manner, your butt is covered. It's only when you pretend not to know what to do that you put yourself at risk.