Or you can use a lazy line.
Fasten a length of rope no longer than the hull (so if it fall under it will not reach the prop) put a clip on the end, when arrive at the choosen mark guesstimate how much rope you need, tie a perfect loop (similar to a bowline but can be tied in the middle of a rope) clip the lazy line onto the loop and let the anchor down with the rest of the rope in a drum inside the boat. Only problem is that it can take up some space on the deck.