For stillwater fishing I think getting the depth right is maybe one of the most important factors affecting one's fishing success. I'd say getting the depth right is way more important than fly selection. Most times the fish are near the bottom or within one or two feet of the bottom. If you can swim your fly within one or two feet of the bottom, you're going to be more likely to get fish to bite. Long ago I used to use the marked rope method, but a fish finder makes determining the depth so much easier. I'd say a fish finder is well worth spending money on, even if it only marks depth and doesn't do a good job of finding fish. It will greatly assist in fishing new lakes as you will quickly learn the bottom contours, whereas with a marked rope method it might take years to really learn a lake's bottom contours. A fish finder will also help you determine the composition of the lake bottom, whether rocky bottom, a hard sand bottom, a soft mud bottom or a weedy bottom. That is important information to know, as it might affect what the fish in that area are feeding on. If the bottom is soft mud or weedy, the marked rope method might give you inaccurate readings. For example, if the mud is soft and your anchor sinks one foot into the mud, you might be fishing with your chironomid pupa sitting on the mud surface instead of above the mud and you likely won't get a bite. On the other hand, if you are intending to anchor and fish chironomid pupa under an indicator, the marked rope method might be sufficient, especially if there are other fishermen around who might tell you the depth without you even having to measure the depth.
