Yes you can use a few staples as you have. They are so small that any rust will not be a problem. I have used a staple or two in tanks which have since been running fine for years.
I hate fishing line, it is a pita to tie. i prefer using either black nylong wire ties or waxed (unflavored) dental floss. Both of these will last until you cut them off. The floss is white and does show more than the wire ties. Also, if you have plecos, be carefull using floss ans they can get themselves tangled up in it.