How to make the horizontal rule behave itself in twenty twelve showcase

Hi and thanks in advance for the help.

First, here’s the page where the problem is occurring. http://www.vonwardkennels.com/blog/sires/ It is under the dog Moose. I am uploading his pictures through the media button, selecting left align for the first pic, right align for the second, left for the third. There is no fourth pic in this arrangement. I am putting these three pictures between paragraph code. It does not help.

Then I uploaded a bigger picture that starts a new line. It takes the entire screen.

Then I added a horizontal rule for a visual break between Moose and Unkas.

The horizontal rule will not stay where I put it! It keeps moving to the batch of three pictures.

I can, but am VERY SLOW at editing css and such but this seems like such a simple process. You put your html code in order that you want it to appear and it shows up in order. Most. of. the. time.

Thanks so much to the person who helps me solve this! I know the sensible thing to do is to just forget the hr but honestly I need to understand why it’s not working.