Hi Bret:
If you're talking about guying an antenna, rope is fine. However, due to
the torquing forces experienced by a tower, you should consider heavy-duty
stranded guy wire and anchors.
The stuff I use isn't that easy to work with, you need to cut it with a
hatchet or chisel or something similar. I got some guy wrap to hold the
wire in place on the tower legs. This stuff won't deteriorate in th4e sun,
although I inspect the turnbuckles periodically to assure proper tensioning.