We already have laws and visas that allow Mexicans (and others) to come to the USA on temporary work permits to work in agriculture and return home. They can come and go legally. The problem is this law is ignored like the rest of our immigration laws.
And the biggest problem is one that's seldom mentioned: far more want to come here to work, and to stay, than anything other than outright open borders would ever allow.
This country will either learn to say no, and mean it, or it will be overrun by illegals from many parts of the world.