Deterrents are not effective over longer term, but exclusion can be! Essentially, with deterrents we're attempting to "convince" a rabbit that something it instinctively recognizes as nutritious food isn't food. There is also the issue of habituation - Even when we can put something stinky or bad-tasting on the food/plant, animals will learn/habituate to disregarding that once they eat of the plant and it still fulfills their hunger. Another problem with surface-applied deterrents is that they must be reapplied to compensate for breaking down in sun (UV rays), being diluted by rain, and continued plant growth (i.e., portions that hadn't yet grown/emerged when the spray was applied). 
Excluding rabbits can be done at the single-stem/trunk basis with either retail-available tree-wraps or homemade cages of welded-wire. Exclusion from broader areas such as around a garden or an entire yard can be achieved by building (or extending) a well-supported fence with unchewable, undiggable welded wire with relatively small (1 inch) openings above ground (2 ft is sufficient) and extending it belowground about 4-6inches - ideally, extending the underground welded wire in an L-shaped "apron" about 6-12 inches would prevent rabbits from digging under- and into/past the vertical fence. 
Other approaches could be seasonal, such as an electrified fence typically used to contain and/or protect free-ranging chickens.