Its funny you should raise this issue of animals damaging tree bark, since just last week i was at a property in Burpengary Nth west of Brisbane looking at eucs with serious bark damage caused by horses.
But back to your issue of squirrels, I'm one of those people who actually loves squirrels (and yes i know they are a real problem in some rural areas) so I kinda think you're a bit lucky to have a family so close to your house...anyhow back to the damage...it would take an enormous amount of damage through the branches of the upper canopy of your maple before it became a serious issue. Post some pics if you can.....
Herbivores of all species do occaisionally chew tree bark, they are actually after the sugars in the phloem not the bark itself which is pretty much useless to them nutritionally, this does cause damage to the biological function of the tree, and its particularly bad for small diameter branches since there is not much volume to start with...bad for those branches but not necessarily serious for the entire tree. As for deterring the critters well there are many home remedies but personally I'd provide them with nuts in a caged bird feeder up high in the maple where you and your family can view their acrobatics as they feed (like I said I love squirrels!) if you make access to the feeder really difficult it cankeep you entertained for the 5 mins it'll take the squirrels to work out how to get them!
Here's some of the pics of the damage I assessed the other week....
