You need to reread my post.  I'm talking about what the law is in other states and what I think it ought to be in Iowa.  In this case (edit: other states where one neighbor has cattle and the other neighbor does not), there is no such thing as "noncattle neighbor's fence" because fencing in the cattle is entirely the responsibility of the owner of the cattle.  The way current law is in Iowa, the noncattle neighbor pays for a fence that is of no value to him or is liable for damages caused by cattle he does not own.