I cannot check, if the newest GarageBand will install any loops with effects, because I have many JamPacks and other music apps installed, and it is hard to say what has been installed by which application. If you type "dog" into the search field in the Loop browser, do you see any effects at all? Make sure, you have the preference > Loops > filter for more relevant results disabled. And the drop-downmenu at the top of the Loop Browser set to "All Loops".
I'm not aware of what iLife '11 is. How do i check this?
iPhoto, iMovie, GarageBand have previously be sold together as bundled applications "iLife". That is why the previous versions in the iLife '11 bundles are named GarageBand '11 version 6.0.5, iPhoto '11 version 9.5, etc. The iLife sound effects were part of the bundle, because iMovie '11 needed them. You can see, if you have a previous installation of iLife, if the Loop Browser has "iLife Sound Effects" in the drop down menu at the top of of the brower.
If i don't, what's the best way to get sound effects like this?
You could buy the iLife '11 bundle. The App Store does not sell it any more, but it may still be available at Amazon or eBay. This way you would get GarageBand '11 with the Sound Effect Instrument, a better iMovie, iDVD, and the loops for sound effects. But it is a bit expensive.
Perhaps isteveus knows a link to download free sound effect loops. I don't remember, where I once found free loops.