1. Boulders.
   • Size: It's easy to overestimate the stability of large boulders, which may be more lethal than stable.
   • Shape and angle: As important as size is the shape of the boulder's bottom, the shape of the socket it is sitting in or the angle of the slope it is on, and the ratio of height to width.
   • Fracture lines: Any rock feature used as an anchor should be checked for fracture lines, which may be subtle and difficult to judge, such as at the base of a rock horn or near the edge of a crack.
2. Chocks. When using chocks for anchors, check to see whether one side of the crack may actually be a detachable block or movable flake; a crack has to widen only a fraction of an inch under the force of a fall for the chock to pull out.
3. Bolts and fixed pitons. Commonly used for anchors. Solid more often than not, but notoriously difficult to assess.

Imagine the hidden undersurface and the block's center of gravity: Will it pull over under a big load? Test it, gently at first so you don't send it over the edge. Occasionally, one has to set up a belay at a jumble of large boulders, with some resting on others. A boulder underneath other large boulders might be quite solid but can be difficult to assess even with careful checking.

Beware of making strong assumptions about what you can know about the security of an anchor based on textbook knowledge and local observation and testing. Virtually any manufactured object used to establish an anchor can have hidden defects, and the usual inspection and testing of natural features will rarely establish their soundness conclusively. For these reasons, the normal practice of most climbers is to set two or more belay anchors for a downward pull.

Do not accept the first anchors that look good enough, but search widely for simple and obviously solid placements. To save time, don't immediately pull out earlier placements that seem less than optimal, as you may find nothing better.