can i do this?

[Karen]

I am very interested in designing dog collars. Like getting cheap dog collars, do my own lil things to them and resell them. Can I do this or am I running into copyright or something like that?

If by "do my own lil things to them" you mean gluing on things like copyrighted logos or cartoons, or other copyrighted material, yes you could be prosecuted for copyright violations. If you are just planning to add your own deigns to them somehow, you'd be okay.