I tend to think rabbit is your most likely culprit, and it really is not unusual to never lay eyes on the little guys. It would be a very normal rabbit to know when you are out during the day. As prey animals they are very sensitive to changes in the environment around them and you make plenty of noises inside the house that they can hear... And they can tell when the house is silent. They are experts at freezing and blending into the background if humans suddenly appear. They also get quite well acquainted with our schedules and will grab a bite to eat when they know we are not usually outside. I once spent an extra half hour outside on a nice June evening at dusk and startled the heck out of two rabbits who frolicked their way up from the bottom of our property to end right by my feet at the clover patch right there. I was also surprised because I assumed they would have come from the much closer tree-farm off to the side. I could tell by their shocked expressions when they realized I was there that they were thinking "you're never out here at this time of day!" Anyway. I had one remaining chard plant in my garden that very slowly got grazed down to a nub, and then they gnawed on the stump of it. So I can attest that my rabbits like chard. A simple solution would be to get some bird netting and wrap it around a tomato cage and place that over the chard plant. Cheers!

Put out some squirrel treats, like peanuts or corn, and some water (e.g., in a birdbath). Are you sure it's squirrels?

haaahaha...i now don't feel so bad knowing that a family of squirrels has taken up residence in my garage. good thing my garage is not attached to the house. but they have torn a huge hole in the back of my garage, and it seems that they are not even scared of me anymore. when i go in the garage, the mother squirrel does not even move from her spot up in the rafters. i swear today that one of them was waiting for me on my back porch....wtf?? thankfully my husband has just bought a giant assault rifle type pellet gun and is excited to use it. the squirrels have done so much damage to our garage, i almost feel like we might as well tear it down and build a new one. they have ripped down ALL the insulation, and the holes are ridiculous. so...good luck to all you squirrel hunters out there...and just remember...they might be cute..BUT THEY ARE STILL RATS!!!!

Thank you so much, Carol, you are the kindest person, and I know you have your own burden to carry. Caring about each other amidst all the bad national and world news is so sustaining and helps in every way. By the way, I can't recall (most things), but have you joined the gardening forum that many of us are streaming to? I loved coming here for so many years, but recent events have left a bitter taste in my mouth. So many of us are over there now, and it's a very friendly and easy to use site. I hope everyone who reads this will wander over there and decide to join. It's the Roses Forum in the National Gardening Association and so many of us have joined there that hopefully you'll all feel right at home. I'll often come back here, also, but too many annoying and frustrating things have happened here, and it's just not a welcoming place any more. So sad, after all these years, but sometimes we're forced to move on.