Simpler to just block everything when risk of LNB bbq exists. Any black
object you use to protect the lnb will need high conductivity of heat
(typically metals) to keep it alive.
This project started as a water heater, so with TV as a secondary
operation one can accept that there will be times when the dish is
unavailable for entertainment. I think a little predicitive programming
will go a long way to prevent problems of the 'the water heater cut off
my show' variety. Logic could go like this ... Time between 6AM and 7PM,
compare dish position and solar position for two hours, alert human if
potential conflict exists.