I don't know what deer fencing is, but if your other poultry have been all safe for all those years.. and the fencing doesn't have something solid across the top of the fence(such as wood or rail).. it should be relatively safe to first clip the peafowl's wings before letting them out.
The idea of clipping is they can't so easily fly far if they happen to do the typical "newly loose" peafowl reaction of freezing, jumping hard, flying non stop until they land in something or drop out of exhaustion far away. Even so, clipping is not really advisable for birds let loose where they can easily hop the fence or there is no fence as this will leave them very defenseless against predators or dogs and they will be defenseless until the next molt, which can be nearly a year if their wings were clipped soon after the annual molt.
However. If there is wood or railing on the deer fence, they still can easily jump to the top railing even with clipped wings. So you will need to be a little vigilant about that and they can be sort of trained to be discouraged from jumping up on the railing by running around and shooing them back in the area every time they do that.
Wing clip only one wing, and also only the primaries- the feathers on the 'hand' part of wing.. these will be the orangish ones on the blue's wing. Don't cut the solid black or the light tan with barring on it(the secondaries). It is the primaries that give the most energy for take off or powered flight.
