Hi...

I think you asked it before... or someone else...
nevermind...

anyway..
some of my lazer diode considerations are:
1)fog
2)humidity on lens
3)flying objects - birds
4)neighbours

I personally used a regular laser diode which you can
find in laser pointers... its very chip.
I amplify the light signal every about 20M
(due to no direct clean path)
about every month I cleaned it.
now Its not working, I have other arrangement.
thats all I can think of now.
goodluck.
OK