My suggestion would be to take in the cattle on a cash basis, getting paid monthly with the money to be paid at the first of each month for the month following. This way, either party can get out in a timely fashion if things don't work out.
I agree with Soapweed except that I would recomend a written contract specifying time frame and who furnishes what such as salt medicine labor for branding gathering shipping etc. Heads off a lot of trouble before you start. Good Luck
After dozens of arrangements,paying cash on a yearly deal was by far the worst for the owner of the cattle.If you have a honest renter fine but know them well! A share contract with a reasonable share for the caretaker worked best for us.Gives the renter an incentive to do his best.
In the event you are trying to fill pasture did you consider just taking in 150 cows? That way it's constant cash flow in the event you have the owner pay monthly or you can do a half due when they come in and the other half when they leave.