Marmaduke plans on taking a new route for his daily drag Owner-Man hour, aka walk. Owner-Man fears that the new route will take them deep into the ocean and that the Coast Guard should be notified if they do not return. But Marmaduke isn't so stupid as to endanger his own life, he's merely taking Owner-Man to a secluded place where things shall be done. Only Marmaduke knows for sure what they might be.
Marmaduke's Owner-Man is exaggerating how much it is raining.