There are no technical bulletins or fixes for this problem. Honestly, I can't think of a way to stop it from happening.

Afterthought:

Did the dealer even say how it happened? The EVAP system is a sealed system.

They thought it was sucked in by the canister.

Is it a 2004 Honda pilot or a Chevy Silverado? Here is your posting

2004 Honda Pilot Engine Problem with 99000 miles
Engine light went on and dealer found sand in evap lines running to vent canister. They blew out the lines and replaced the canister, vent solenoid and purge solenoid. How do I prevent this from happening again when I drive on the beach. The car is rated for light off road. Sand should not have been sucked in but I read that the Silverado had this issue and GM issued a fix.
Asked by (pending member)

On the Silverado GM moved the vent valve. I am not sure where the Pilot vents. Is it at the valve or the canister? Subaru vents at the canister. I could put a piece of foam over the opening as a filter if I knew where it vents but this could interfere with the evap operation. The shop manual is not very clear.

Any suggestions?

I have a 2004 Honda Pilot. I am using the Silverado as an example of a similar issue and how GM fixed it.

how deep did you get in the sand?? the vent valve is normally open but have to be pretty deep in to get sand in the system which would put the responsibility back on you.

Roy

This vehicle is rated for off road. The canister should not be mounted in an area that can be exposed to water, dirt and sand. This is a design flaw.

its all about the vent valve as that is the only entry point

Roy

Refer to diagram. Hose " B " is the vent hose and is the only link externally. It is either plugged into a one way rubber grommet or clipped to frame and left as it is. If you follow the line, you should come to it.

You can get a minifilter to be capped onto it. Extending the hose and relocating it to a higher leel would help.
You mentioned it is for light off-road but if you are doing it more than lightly, the problem would occur as it is not an instant occurrence and would take some time before the sand gets to sufficient volume to be sucked into the lines.