It is more likely that you would come upon Fort Rosecrans on your way to Cabrillo National Monument, and for more information have a look at my Cabrillo National Mounment page.
However, if your original destination is the cemetery, you may include a visit to Cabrillo National Monument and the Old Point Loma Lighthouse for more San Diego history and a different perspective of the views.
The old lighthouse sits high at the top of the peninsula and one a clear day it is easy to see from the sea. The problem is that this area is usually covered in cloud during the evenings and in the mornings. The light was obscured and not useful so it had to be abandoned and another was built at the base of the peninsula which is much more effective.
Another side trip from Fort Rosecrans is just past the cememtery and down the hill from the road. You'll find the operational lighthouse and the tide pools. At low tides it is fun to climb down the near-by cliff path and check out the tide pools.
Until recently the road to the new lighthouse and tidepool was free. However, this past year the toll booth to Cabrillo National Monument has been moved down the road, just before reaching the turn-off to the tidepools. The good news is that the entrance fee has not increased. It is still $5.00 per car. If you come on your own, by bicycle--a daunting task--or walking--an awesome feat--the fee for an individual is $3.00.
You might consider checking the time of low tide for the day of your visit. The area is beautiful at high tide, but much more fun at low tide when you can climb down the cliffs to water level and spy on the creatures caught in the pools. Besides seeing various anemones and starfish, I have seen the "spongy deadman's finger," shellfish, including crabs and in the early days of my youth--before all the rules and regulations against removing anything from a National Park--I actually caught a baby octopus and a little seahorse! I took them home to become my beloved pets. Instead they quickly died. Now that I'm no longer in the third grade, I understand the importance of leaving the flora and fauna where they live. Just seeing the animals of the ocean are thrilling enough.