This is another one that’s easy to make. That’s because it’s should follow the rule of using an apostrophe to convey the possessive form (as in the dog’s collar). But in the case of it, an apostrophe is used strictly for the contraction of it is or it has (“It’s the dog’s collar.”) while the possessive form has no apostrophe (“The dog is wearing its collar.”). The device you can use to make sure of proper usage is to imagine replacing your instance with it is or it has. If it doesn’t make sense, you don’t need the apostrophe!