Date, considerations, meeting of the minds (you, all land owners) is a voidable contract. The notary would make it better if contested. I would get an estimate of the cost of the fence(or total cost period) and put the number of years/months on the contract. Here is an example and you could add to if you want. Maybe add who is responsible for repairs, maintenance, act of God, in-depth description of the fence etc.
Date______________________________
I ___________________________________(you) agree to build a fence on property located at________________________________________________ (property address here) and our agreement is I pay for the fence cost __________________(fence cost here) and the cost of the fence will go to the number of years/months my rent will be paid in full___________(years/months here).
Renter Signature__________________________________________ Landowner Signatures___________________________________(all owners) very important
Noterrized______________________________________________________________
If not Notarized get at least two independent witnesses that are not a conflict in anyway.