Does a D photo card get old, worn out?

You don't mention what kind of lens, but when my shots won't focus, the first thing I check is whether the lens inadvertently got switched from AF (Autofocus) to MF (Manual Focus).

Are you hearing the beep indicating the lens/camera have achieved focus before pressing the shutter?

Do you hear the humming of the lens as it works to make focus?

Maybe your contacts between camera & lens got dirty and aren't transmitting to each other well?

What settings on the dial are you using to shoot? AV? TV? M? or do you leave it on fully automatic? Possibly a slow shutter speed setting is giving you these results, especially with animals on the move.

Lens damage is a possibility but I'd check the simple things first. Even us seasoned photographers muss up by not double checking the settings.

My 24-105L Canon lens was dropped by a friend who thought they were helping by picking up my camera bag/sling. I had not zipped the cover back up as I was in a hurry to get my camera and take an action shot. When they picked it up the lens fell about 3' to concrete. No damage other than a scratch and as sharp as ever. Very lucky, I was!

Probably not the memory card. Easiest first step, as someone else suggested, is make sure MF-AF switch on lens didn't get set to MF. Then try another lens and see if you have the same problem. If second lens test is OK, then problem is the first lens that got dropped. And if that lens is an EF-S 18-55 lens, double that possibility. They're very bottom shelf, despite the Canon name. IMHO.

This sounds like a focus issue. It definitely not a bad memory card. Here's a quick tutorial on checking your lens for focus issues. You can also search Google for "front back focus issue" and find some printable charts to test with also.