Roof anchors are divided into two camps... anchors that are great for new construction and those that are awesome for existing construction. Today, we'll be discussing the latter because quite frankly it can be pretty difficult to find a decent anchor for existing roofs.
There are two anchors I'd like to introduce you to today. Both are excellent options for pre-existing construction.
Guardian Halo Anchor: This guy installs straight through your shingles and substrate. Sure, you'll have to plug holes when you leave (there aren't very many holes), but this anchor is completely reusable. I think I just heard your pocket filling up. The fasteners are included and it fits on any pitch.
Want a more permanent solution...
The Guardian Ridge-It Roof Anchor or the French Creek Permanent Anchor are great solutions. All you need to do is pop up a bit of the ridge cap, pound this anchor into a truss, and put the ridge cap back on. That's it! These anchors fit any pitched roof, come with required fasteners, and can be left in place for maintenance. It really is a nice option to have.
So, there are two options for one of the most frequently asked questions on this website.