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=I would not be hesitant to keep poison in the compartment as it doesn't work until the mouse drinks water which should be outside the spa.
Not sure about that....are you using the Decon type? As far as I know, there are only two major styles of killing rodents. Neither one has anything to do with drinking water. What is the active ingredient in yours?
the real venerable spot on the Marquis spa is behind the outside light that lights the entry to your spa, if you put a screen there and as with any other spa the opening where your flex conduit comes in you should be fine but rodents can find a place that would surprise all of us but you should for the most part be fine if you put a screen behind your light and take care of the flex.....