What could cause my urine to stay dark and have a strong odor? I drink plenty of water but it seems like I stay dehydrated.

Dark urine. Are you taking any vitamins or supplements? Generally the more water you drink the less concentrated your urine should be. You might want to have your urine checked at your doctors to make sure there isn't anything else going on. But do check any supplements or vitamins you might be taking the b complex vitamins are famous for causing bright yellow urine with an odor.
Be seen. It could certainly be dehydration, but there are many other things that can cause your urine to appear dark, from proteins or blood. You need to be seen to determine if other problems are at work.