In recent years in the US, to say someone has "been around the block" is not positive. It has come to often mean that the person is experienced sexually. "He/she's been around the block a time or two" is the common expression for this. I would no longer use it to mean that someone has professional experience in their field. They would not appreciate it.
If you want to say that someone has a lot of experience in a certain field, then just say that. "I realize that you have a lot of experience in xxx."
Some people, e.g. a contractor, when they are questioned re: their experience will make the off-hand remark, "Well, you know this is not my first rodeo." (Meaning, "I know what I am doing.") (Then, in this type of off-hand, very informal situation, a person might add, "You know, I know what I am doing. I've been around the block a time or two.") But only in this type of situation. Otherwise, I would not use this expression to show professional experience. Also, note that it is the contractor, for example, who makes that comment about himself. Not someone saying it to him.