Homeless people do not have the right to sleep on private property. It's private property. I've already said that this is a supremely dickish way to get people off your property, but that doesn't mean they're infringing on someone's rights.
Sorry...but people don't have the right to trespass on private property. So what peoples' rights are you talking about?
I was just replying to Alex's post in general. The way he worded it, I actually thought, he acknowledged that there was infringement of citizen's rights.
But anyway. In German constitutional law this could have been broken down to a few competing rights granted by the constitution: The general freedom of action vs. the property right of the owner. Then again, an infringement of the former can only be disputed, if, indeed some sort of governing authority has caused the infringement, unless it's a crime, which is not the case here.
Then again, if someone chose to destroy the spikes as a political statement, believe it or not, one could think about bringing freedom of speech into play. Or freedom of art, depending on what is done. The right of protection of your property can be limited by other constitutional rights in my country. It's not really the strongest protected right in our constitution. It always depends on the single case and circumstances, of course.