Patience is a virtue when anchoring. Do not consider the anchor set just because it has touched bottom. Finally, deploy the desired scope needed for your particular anchor and rode makeup. If your anchor was chosen to match the sea bed and still hasn't set after a couple of careful tries, it may be fouled and should be retrieved and cleaned. Fouling of anchors can come from a variety of sources, both natural and manmade.
Rocks can wedge themselves between flukes and prevent penetration.
Having established a secure anchor set, you are still not through with securing your boat. Belay the rode onto a capable Samson post or cleat and apply effective chafing gear in strategic places to protect it during the multitude of boat motions that will take place before you are ready to weigh anchor. Leather, canvas or patented anti-chafe tubing are useful. You are still not free to ride your dinghy to shore for the planned barbecue for there is the matter of swinging at anchor, called sailing or horsing, which occurs with both sail and powerboats. Winds are never steady in strength or direction and they can cause it to sail back and forth, possibly sweeping 30 or more each side of a nominal position.