The yellowing looks abiotic in cause, which means it would be due to non-living factors like environmental conditions (as opposed to a pest or disease). Stress from growing in a container is likely a contributor, either from heat alone, soil drying or over-watering (more likely the former), or running low on nutrients. Nitrogen depletion, for example, is a common trait of container-grown plants, since it can leach out of the potting mix when plants are watered often. Your application of fertilizer may help, though it might not take effect immediately, and leaves already in the process of yellowing won't green-up again, since they can't physiologically reverse that process once it starts. You can let the potting mix get fairly dry to the touch about two or so inches deep before watering should be needed (monitoring depth depends on pot volume size, which is hard to judge in the photos). The bigger the pot, the deeper you can let it dry between waterings, at least to some extent. Make sure it's not sitting on a saucer that will collect drained water (or rain), as this could seep back into the drain hole(s) and saturate the lowest layers of soil in the pot, potentially killing roots.

As you alluded to, growing figs in the ground is best since it provides them with much more root room, less soil temperature and moisture fluctuation and stress, and more consistent nutrient levels. If deer and groundhogs are problems, you could try putting up fencing around the plant to protect it, since scent barriers like scented soaps don't tend to be as reliable as commercial repellents, which in turn are also not as reliable as a physical barrier like fencing. Deer usually don't like plants with the kind of latex sap that figs have, though it's not unheard of. Aside from keeping it potted, if fencing an in-ground fig is not an option, we don't have other suggestions other than what you are trying (keeping it more out of reach, plus using repellent).

Miri

Thank you for your thorough response! 

You're welcome.