We very frequently fit high quality mesh to the louvre windows of church steeples and spires. The reason for this is invariably to keep pigeons / crows / other birds out.
We use 1 inch x 1 inch heavy gauge galvanised mesh, but we can, and sometimes do, source and fit stainless mesh, which is what you will want if you want it to last forever (but the galvanised stuff is so good that it will last a lifetime).
We do not fit chicken wire or any other rubbish that will rust and rip within a very short space of time. You will, however, find plenty of other contractors that do.
We also fitted the permanent ladder seen here – more information can be found at the following link – Installation of permanent ladder and louvre windows mesh