First you need to check if he/she really has oral ulcer. Sometime the oral cancer has the symptom as ulcer. The symptom has been on and off for two years, which is worth of some attention. Any special dental hospital is able to diagnosis with a simply biopsy. Sorry to answer this way. After eliminating the possibility of cancer, the rest is typical oral treatment and management. As elders, vitamin deficiency is very common which could cause ulcer too. Good luck!