Hi Hisham, The idiom here you are using is "to no avail" which means "unsuccessfully" or without achieve what you set out to do. I believe it would be more grammatically correct to say; " I spent two hours explaining it to him, but to no avail."

Hello Hisham, sorry for the late reply. I had a death in the family. To answer your question yes, it is natural and something we say. Another, more natural way is to say: "I spent two hours explaining to him and he still didn't get it." Although your saying is natural and good, this saying is better and something we say more often. Hope this helps and feel free to ask for help anytime. I'll do my best to help as promptly as possible.

I'll help you if you take a trial lesson.