McCarthy admits it is "unacceptable" Wolves have given away four goals from dead-ball situations already this season - versus Blackburn, West Ham, Sunderland and Portsmouth.
Now they have to combat the menace from similar situations of Villa who have scored nine of their 12 Premier League goals this season from set-pieces mainly via the deadly delivery of Ashley Young.
McCarthy said: "We have got Villa and Stoke coming up in successive games and they will both be a real potent threat from set-pieces.
"Villa have got nine out of 12 goals in that way. Young was a £10million player when Villa bought him and he has improved since then.
"I would expect him to put good deliveries in and, with John Carew, Richard Dunne and James Collins good in the air, they have certainly got a very potent threat.
"How do you stop it? The goals Villa got against Chelsea came from free headers. Stopping them having free headers would be a good start! That is really the essence of it.
"A lot of people get wrapped up in trying to stop the guy heading the ball rather than heading the ball themselves, and in trying to block him off, they only have to slip, or lose the player for a second, and it's in the net."
McCarthy added: "Am I happy with our set-piece defending? Overall I am happy and yet we have conceded four goals - Blackburn, West Ham, Sunderland, Portsmouth.
"It has been individual errors. It is not acceptable at all."
McCarthy is looking to record signing Kevin Doyle to continue his fine form after a hernia operation delayed his debut following a £6.5 million switch from Reading.
Doyle scored his third goal since proving his fitness in last weekend's creditable 1-1 draw at Everton.
McCarthy said: "I knew what I was getting when I signed Kevin and he has been everything I thought he would be. He is a great lad around the place.
"He can play different sort of strike partners, no problem. He is a good footballer, an intelligent footballer. I am delighted with his form in general.
"He has played well and scored goals but he is a likeable character as well."
McCarthy knows Wolves have to improve their home form and they have collected only one point from the clashes at Molineux with struggling West Ham, Hull and Portsmouth.
He said: "I am not happy with the home form. We want to get more points. But it is how many points you end up with, not where you get them.
"We played well in the last game at Everton. Overall we have played well. The performances have been good. Maybe we have not got our just desserts."