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Resource guarding is a fairly normal, but undesirable, behavior. Fortunately, it's generally relatively easy to fix. See this thread for information: Resource Guarding, causes, prevention and modification
There is a difference between dealing with the behavior in the moment (the corn cob incident) and training to mitigate the issue. Your instincts with the corn cob were good; one suggestion would be to toss a treat away from the object so the dog chases it and you have a chance to grab the item. For training scenarios, you want to move much more slowly. The info in the link above provides good instruction.
Resource guarding is a fairly normal, but undesirable, behavior. Fortunately, it's generally relatively easy to fix. See this thread for information: Resource Guarding, causes, prevention and modification
There is a difference between dealing with the behavior in the moment (the corn cob incident) and training to mitigate the issue. Your instincts with the corn cob were good; one suggestion would be to toss a treat away from the object so the dog chases it and you have a chance to grab the item. For training scenarios, you want to move much more slowly. The info in the link above provides good instruction.