If a decree has not been signed by the judge, then it has not been filed, and has no binding effect on anyone. The circumstances and length of the trip would be relevant - as would the myriad of other factors that play into custody issues. If you are the custodial parent, then there are Temporary Orders in place, and if dad wants to claim custody, he should be prepared to start the litigation from scratch. A short trip out of town is unlikely to impress a judge as a basis for changing custody.
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I agree with Attorney Langford. Even though you've got a final decree filed, it's not enforceable until the judge signs it. If you have some temporary orders in place, those are what will control custody. The only way he can use it as a basis for custody is if you're on an extended trip-- at least a month. At that point in time, he might have a basis. But not for a short trip.
If the judge has already made a final ruling then he would have to file a motion for reconsideration or a motion for new trial to change custody. Simply leaving for a vacation is not grounds for him to get custody. I would put it into an email that you are requesting make up time or a switch in weekends. Some parents thrive on documenting each time you don't have the kid in order to build a case to fight you later and claim he had the kid 50% of the time. If you currently have temporary orders determining custody and visitation then a simple call to the police will get your child back. Good luck!