Squirrels. Definitely.

It's funny but sometime last week, my sister and I were on the way out from my place and we saw a squirrel running across the parking lot with a big wad of what looked like toilet paper in its mouth, with a long piece of the paper dragging behind it. The squirrel stopped briefly and then headed over towards one of the lot's chainlink fences. As it started moving again, we watched stunned as a pile of "bite size" style chocolate chip cookies suddenly began to fall out of the back of the wad that the squirrel was carrying, leaving a trail of now-lost loot!! LOL I have seen the city squirrels here munching on discarded bagels and chicken bones, etc.

Nuts? Who needs nuts? :-p

Only thing you can maybe do is try to net your containers or put some mesh or chickenwire, etc., just under the soil (allowing the plants to grow through it and covering it with soil or mulch to hide it), in order to try to deter the squirrels from digging. Some might recommend trying products like Liquid Fence (which is an all-natural blend of various things like garlic, cinnamon, citrus oil, etc) to spray on the plants... Alternately some might recommend hot pepper spray on the plants, although nature lovers don't seem to like that recommendation as it can cause them to burn their eyes.

Squirrels can be a royal pain for container growers and ground gardeners alike and there have been many many threads on GW over the years with suggestions for deterring them (including the oft-mentioned pellet gun... ;-)).