Read the can. They vary in their recommendations. I used to work in a hardware store and would get this question every spring. Most say two coats to last 3 to 5 years. But more coats doesn’t mean they will last longer.
Read the directions on the can!!! Any kind of coating is only as good as the preparation done on the surface it’s being applied to, Clean, lightly sand and get all the dirt off and prepare the area around the project before opening any can of whatever paint or sealer your using!
then you perhaps can get a good life out of the job your doing…