AC coupling will block the DC of the sun. it does not matter what you do if your sensor is non directional though.
drive your emitter with an oscillator and put a capacitor in the receiver analog electronics. a tube on the receiving end will make sure the receiver is in the shade and might be enough for your system to work as it stands since you say it is working when the sun is not out.
while you do not need a laser it could make it easier if you are looking at long distances and certainly a visible pointer for a source makes it easy to set up
dan