Love that reflector idea. You are so right, most boats do not offer up a strong reflection. I have a Lowrance HDS plus HD Radar - the combo is amazing. Especially when combined with the point 1 option to overlay the radar over your chart plotter maps. Cost wise, cheap insurance. The HD Radar was about $1200. Harbour Chandler is where I get all my electronics.
This is a great thread as it is helping create a lot of awareness about just how dangerous it really is to run in the fog. I have had a few close calls. All have been with boaters who are running at full tilt using their GPS chart plotter with NO radar. GPS is not a navigation tool to be used in isolation in foggy conditions. In fact I believe the advent of GPS has actually increased the danger of collision due to operators who have their confidence artificially bolstered.
Like I said earlier, I think the collision regulations need to be modernized to recognize this particular flaw in the mindset of most boaters.
My best practice/advice is buy a radar unit, slow down and keep a close watch. I'm also an advocate of installing AIS, particularly for anyone who is operating off shore in the shipping lanes. Radar really is no good to you unless you are paying attention all the time.
I talked to a guy in my marina who scoffed at installing AIS (he had radar) until he was almost run over by a 900 foot freighter. He said that when he first noticed the freighter it was so close that the radar reflection off it was scattering the signal and it was impossible for him to figure out which direction and course the ship was on...until it was too late and drove right by him within 100 feet. Way too close call. He now has AIS.
Oh ya, in case you think..."I can out run any freighter" check out on AIS just how fast they are running - most are going between 15 and 23 mph...I seriously doubt you can get out of their way once they are inside a mile unless you know exactly what course they are actually on.
Again, how much is your life worth? Pretty cheap insurance really.
My 25 cents.