I just picked up the messages from Don. I will try those suggestions. I'll let you know what happens.
By the way, I have another little site hosted by the same host, so was able to pick up their standard 404.shtml file (there was none for 403s) and took a look at it. I think they coded it wrong. It is html code; has the beginning html, head, title, body codes, but does not have the ending body and html codes. I wouldn't think it would work without them. So, I added them and put that file in my other site, added the needed coding to the htaccess file, cleared the cache and tried asking for a non-existant page. But the 404 "file not found" page I got was not the file that is in the 404.shtml page. It appears to be the standard Apache 404 error message. Don't know why the server did not see the custom page. I put it in both the root folder and the public folder. It didn't make any difference.
Yesterday I put all my user agent blocks and referer blocks in the public htaccess file. They are all getting 500s. I'm gonna try Don's ideas.
I'm going to experiment a bit and see what happens. I'll let you know.