Here is the sentence again:
The blank space between goes and at causes a fused sentence. At this spot, there are two complete sentences joined with no punctuation, which makes a major error. He insists on wearing socks everywhere that he goes is a complete sentence. At the beach, in the shower, or around the house, you will find ... begins the next complete sentence.
To fix this problem, you could put a period after goes and capitalize the A for at.