How about if Tad just tells his son he has some errands to run. That way the boy doesn't really know where his Dad is going, and when his Mother asks him, S just says, Dad said he had some errands to run.
That way it keeps the S out of the middle and Tad doesn't have to have a confrontation with his W over it.
With cell phones there's no reason Tad has to give his S info about where he'll be.
