Most boats use an anchor line--called "rode"--that combines line with a length of chain at the bottom. This bottom chain protects the line from rocks, shells, or other objects on the seabed that could cut into the line. It also creates a curve in the anchor rode--called "catenary"--that helps keep your boat anchor dug in. This one factor makes the difference in all of boat anchoring.
You want the part of the anchor rode nearest the bottom to stay as close to horizontal as possible. That's what keeps your anchor buried and prevents dragging (the anchor breaks out of the seabed and bounces along the bottom).
In normal anchor situations, use a bottom length of anchor link chain equal to your boat length. But in tight, or exposed anchorages, double that length. Carry an extra length of anchor chain aboard equal to 2X your boat length. Put Out Two Anchors
Drop a second anchor to decrease your swing circle, or if you expect heavy weather. The text book two-anchor configuration shows a 60 degree spread between two anchors from the bow.
This may work if you have the room to put out another anchor that far from the first one. But what if you don't? Use a tandem anchor configuration. Tandem means "in-line". Think of two plows hooked together. If the first plow starts to move, the plow behind it serves as a brake.
That's just how tandem anchors work. The second anchor uses a short length of chain and gets shackled to the crown of the first anchor link chain. If the first anchor begins to drag, the tandem anchor digs in to save the day!