I used to plant my daffodils, tulips, and other bulbs in the fall, enjoy the show the following spring, and then forget about them when their leaves died down. All too often I was reminded of their location when, while doing some digging later in the season, I sliced through a group with my spade.
To protect my bulbs from accidental injury, I now set them inside plastic flowerpots and plant the bulbs—pot and all—so that the rim of the pot rests just below the soil level. I use the black plastic pots that nurseries sell their plants in; I usually have a stack of them lying around. The larger ones are about the right depth for most bulbs. I put about 3 inches of soil in the bottom of the pot, mix in fertilizer, and place the bulbs on top. Then I set the pot in place and backfill the remaining soil into the pot. I haven’t noticed any overcrowding due to multiplying bulbs. If I do, I just lift the pot and divide the bulbs.
Now if I hit a plastic pot when I’m digging, I know that there are bulbs below. As a bonus, gophers and moles can’t get to bulbs protected by the pots.