One of the biggest defenses on contempt cases is beyond the order being ambiguous or factual about whether the Defendant violated it or not it would be the inability to comply. It is clear in the statute that the Defendant has the burden, but he/she can show that he/she cannot comply with the pre-existing order. Even if the order is unambiguous, the person has an inability to pay. For example, they are supposed to pay spousal support, they lost their job, they have not qualified for unemployment and have an inability to pay that might be a defense depending on the circumstances. Another one might be an inability to comply, so there might be circumstances where somebody is in the hospital and is not able to go to a visit or facilitate a visit because of a medical issue or some other circumstance.
Another defense is that the other party agreed or waived that so that even though there is a visitation scheduled for a certain day, the parties had agreed to change that.