There are a variety of reasons:
Yes. I guarantee that I will trap all animals that are present in your yard for two (2) weeks from the time I leave your yard. I cannot prevent intrusion from other like species after that time.
Generally kick up dirt between the edges of your lawn and hardscape (edges of concrete, rock walls, rock or gravel walkways). They may also pop up in the middle of your lawn which may lead you to believe you have a gopher. Moles will also have "feeding runs" close to the surface which looks as if a snake has moved through the soil. Moles make raised mounds of dirt which are circular at their base. Due to their feeding habits, Moles will generally move around the entire lawn/landscaped area.
Generally a gopher operates in a 5 yard radius. Their mounds are traditionally fan-shaped. If you look straight down on one you will see a plugged hole with a "c" shaped fan of dirt in front of it. You will normally see other mounds or plugged holes in close proximity. You should note that the plugged holes will have small round or oval shaped dirt clods in them. The dirt clods are made by the gopher scooping the dirt with their front legs. Moles do not make these dirt clods as their front feet are not shaped the same as gophers.