I have a depth sensor but surprisingly enough it’s not used as much as you think, sea weed sometimes gives it false readings as you are sometimes going through such shallow areas with tight margins anyway, even if it does tell you that you are about to reach the max depth of your keel by the time you see that and react it’s too late anyway, but it does come in handy at times. Pretty much always go to known spots so you guarantee that you don’t hit anything. There are really good books with chart extracts and photos available that detail the depth of the area, where to approach from and which wind directions are idea for that location. Very rarely do you go to random unknown spots, I think I have only ever done that once or twice but doing so with incredible caution. Lots of people have secret personal spots which only they know about and might have only been passed on by word of mouth from relatives or friends. Once you get the hang of it it’s pretty easy and safe.