I read an article where a creationist disputed dendrochronology by saying that some years trees produce more rings and some years they produce fewer. So you can't just count the rings and assume they add up to an accurate total of years. 
Fair enough to bring that up. Scientists actually do take that into account. Scientists know what kind of trees produce more rings in a year and which produce fewer. For example, oak trees almost never miss a year, with only one year on record without a ring--1816 CE. (See "The year without a summer".)
But the guy was, first of all, agreeing that the tree rings did have a relationship to a specific number of years. This was a fact that people figured out by scientific investigation, but was somehow missing from the bible. And, if people had just accepted the bible, they never would have looked at the tree rings to begin with.
Secondly, as has been pointed out here before, scientists have cross-checked the measurements in several different ways, getting more and more refined with computers. It's not based on one guy eyeballing the rings on one tree and saying, "That's it, proved our case, no need to look any further!" Or more likely, have people keep counting tree rings until they get the count you want, and ignore all the others.
Even still, if the tree ring counts were all over the place, and did not make sense in light of ice cores, carbon dating and other measures, scientists would discard them. But data has been collected and cross-checked, over about a century, on thousands of trees in locations all over the world, revealing evidence of 26,000 years of tree growth. Since the tree rings, the ice cores and other measures all say many more years than creationists can handle, the creationists want to discredit all of them. But they cannot, because besides their ancient texts, they have no data
. And besides, dendrochronology is used to accurately date European church buildings and religious art with wooden panels-- and religious leaders accept those dates as true. So, there.
It's like a crazy hoarder family swearing that everyone lives the way they do, but adamantly refusing to go into any other homes to check and see:
"The way we live is the only way to live. Everyone lives this way. Nobody can survive without lots and lots of stuff packed into your house."
"Many people don't have homes packed full of belongings from floor to ceiling in in every room," you say. "Here are some photos. You can also see how other people live on the internet and on tv."
"Lies, all lies. You can fake photos. You can make up anything on the internet. The way we live is the only way to live. Everyone lives this way."
"Okay, then, come out and visit my home next door, your other neighbor's home and then look into some houses across the street and see for yourself. We can go into all the homes you want, anywhere in town."
"We don't need to visit any other homes. The way we live is the only way to live. Everyone lives this way. Case closed." Door slams shut.
Imagine if creationists tried what scientists do, cross-checking their ideas about the world with other religions and throwing out what did not match with Santeria, Hinduism and Islam. Instead, they assume they are correct from the start and only accept data that confirms what they have already assumed is true
. That ain't science.