There are two sides to the coin of managing fish. One is ensuring there are enough nutrients and minerals to support the food chain required to support the standing weight of fish that you desire. The other is ensuring that there are not too many individual fish to grow them to the size desired.

I empathize with both you and your dad. I imagine that he had a conversation recently with someone. Perhaps it began with "We keep throwing money at this pond and getting less than the results we are looking for. Its growing old." That someone might have discussed harvest management with him. Harvest management seeks to achieve balance such that ponds food chain is sufficient to meet the size goals of the fish you guys are trying to grow. One of the best diaries here on the forum is that of Bocomo's which records the success transition of pond like yours to one that produces some nice fat bass in excess of 4 lbs. You can find Bocomo's thread here.

If after reading it you like this approach to improving fish condition then you and your dad will have some common ground. It could be a project that will offer opportunities to create some great memories together. I wish you the best on this.