They get their nutrients from the water column so don't actually need to be anchored. You can use superglue - just don't use too much as it goes white under water.
I get steady stream of new ones appearing, so what I do is sit them on the substrate and anchor them with a long thin pebble on part of the rhizome. You can also jam the root with two rocks in a harmless squeeze. They'll get 30 cm tall and round, sometimes taller here. It can be a large plant and a beauty.
I keep a roll of thin lead free solder, and wrap a 1 inch piece around the rhizome, and it will sit anywhere you place it... unless of course your fish are landscapers, then they have a tendency to move them around...