Step 1: Find yourself some tinfoil / aluminium foil
fold the tinfoil / aluminium foil to double the depth you want you scope protector to be and continue folding it over itself until you cant go any further. Then simply fold it horizontally in half.
Step 2: Fit to size
TIP make the band very slightly longer then the actual sight so that when you wrap this with tape it will still fit. Be very careful when doing this as you don't want it to be to loose on your scope.
Step 3: Duct tape....duct tape....duct tape....
place your band onto the duct tape and begin to roll the duct tape onto it (place the bottom half of the band slightly above half-way but don't forget to leave a little bit of tape at the top to fold onto the "lens")
Next cut strips down to the tinfoil into the duct tape all the way around but not on the shorter side (see pictures if confused :P)
TIP If the duct tape you've left at the top to fold over the lens is too thick ( i.e it will cover up too much of the lens) cut the excess off as seen in the picture. Remember though you can always take away but never add back!