Idaho Code § 35-103
When two or more persons own land adjoining which is inclosed by one (1) fence, and it becomes necessary for the protection of the rights and interests of one (1) party that a partition fence be made between them, the other or others, when notified, must proceed to erect, or cause to be erected, one-half (1/2) of such partition fence; said fence to be erected on, or as near as practicable to, the line of said land. And if, after notice given in writing, either party fails to erect and complete, within six (6) months time thereafter, one-half (1/2) of such fence, the party giving the notice may proceed to erect the entire partition fence and collect by law one-half the costs of such fence from the other party, and he has a lien upon the land thus partitioned.
Idaho Code § 35-103