There is a way around it; I've seen other phpbb forums where if a stretching like this occurs, it will only affect the post with the long text in it, leaving all the others alone.
It's just a modification of the theme.
Every one can wrap text or cut image in own post but if someone else post long link or too big image then theme is broken again. I am comming to read this forum from three different computers and independent of resolution I have broken theme or not. If I am right only Bondings can solve this problem but not so easy.
The problem is depending on the resolution (or window width) so it's hard to know what is too wide. A small monitor will get this problem with quite reasonable image/link widths. Often this problem doesn't occur with links because they often contains a lot of / which allows the link to wrap.
What I could do is to check for very long url's and replace the visible url with something like "Long URL", while keeping the actual link.
There are a few topics that have one or more very wide images and cause problems. However as this isn't a photography-oriented or wallpaper-oriented forum, I don't think it matters that much.
The problem is - simply put - that an element on the page is very long and hence the page needs to be that wide. This can be a very long word (random characters usually), a very long url or a very long/wide image.
If this is really an issue and given that this happens so rarely, couldn't it be added to the moderator "report" button. So that mods can edit it out manually, assuming they don't notice themselves?