Answer: It's possible the rock salt contaminated the soil, but you would think after three years it would have leached out of the area. I think the best thing to do under the circumstances is to have the soil tested by a lab. Tests will show if the area is too saline to grow anything. If so, removing the soil and replacing it with soil from another part of your garden should solve the problem. If nothing is growing there now, that might be an indication of excess salt. Usually if nothing else, weeds will grow...
The only other option would be to build a raised planter in the area and fill the planter with fresh garden soil, then plant your Lady Banks rose in the planter.
Best wishes with your landscape!
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