If you do not want to remove your horses from the pasture that you are renting any time soon I suggest that you have a written lease with the current owner for a set period of time, for example several years signed and dated by you both. If the property is then sold, the new owner takes title subject to your lease in place for its duration so long as you are not in breach of it.Right now, since you are on a month-to-month oral lease, the current owner can simply give you 30 days notice to end your lease and you would have no legal recourse from what you have written in your question.