What kind of plant are you trying to anchor? If it's a stem plant, I find that removing the lower set(s) of leaves and planting it as deep as possible in the gravel seems to work. Sometimes if you plant too many stems together, the middle ones will float back up, so I generally only plant 3-4 together at the most, and then plant more right next to them.
If it's a rosette plant (like a sword), you don't want to bury it deeply. The area where the leaves are formed (called the crown, I believe) needs to remain at least partially exposed. It can help to place some rocks around the base for a week or so until it starts to take root - this helps prevent fish from digging in the gravel near the plant and dislodging it. Plants like Java fern can be tied (gently) to rocks or wood with black cotton thread. As the plant takes hold, the thread will disintigrate. By the time the thread is gone, the plant will be firmly attached.
I'd leave the daughter plant attached to your sword until it's a few inches high and has some roots of its own.
