The roots of Strelitzia nicolai are reputed to be both aggressive and hard to dig out. It is also recommended to keep them away from any pipes used for either water or sewage. 4-6" of concrete might be enough to keep the roots under the paving - though it doesn't seem to slow down bamboo ;).

Cannas also clump up vigorously...

If you were to sink a semi-circle of concrete to contain the roots - where else might they forage for food and water???

If you do decided to remove the bird it would probably be far less effort if you were to ask your paving contractor to do the job with mechanical assistance rather than tackle it with just hand tools.

A friend of my husband's put in new water & sewer pipes when they moved a mobile home onto undeveloped land. He swears by putting rock salt around the pipes & around plants you don't want 'traveling' before covering up.