At the rentron site, read on to the next section. Uses IR to help with navigation. Even IRs will give trouble in bright light.

You might try lasers, pulse at a high frequency and the receiving circuit set to only respond when the magic frequency is seen.

FREQOUT and COUNT

You could also try shielding the LDRs with a tube of some sort so light can only come from one direction. I tried something like this on a solar tracker. Used a cigar tube. At least the cigar was good.