We planted two plum trees in the back yard about four years ago. They are in full sun and did flower every year but we haven't seen any fruit. They get plenty of water and are not showing any disease. We have plenty of bee and wasp activity around the house. Is there something I'm not doing right?
Where are you located? Fruit trees need varying amounts of winter chill hours in order to produce fruit. If you are in a warm winter climate, they may not be getting enough winter chill. Or, if you've been getting early spring cold snaps, that could be damaging the baby fruits.
Do it right from the beginning if you only want to do the job once. It'll be cheaper in the long term.