If the owner of the property claims that there was no danger before the accident happened, it is up to the injured person and their lawyer to prove that the property owner knew or should have known about the danger. The injured person will need to provide evidence that the property owner knew or should have known about the danger before the accident happened. They may need to provide witnesses who have seen the property owner doing work on the property in an unsafe manner.
This may be a difficult situation, but if you believe you can prove that the property owner knew or should have known about the danger, you should contact a lawyer immediately.