For example in Scandinavia you can't fence your property without reasons and there are some limitations of what you can put there. Are there any limitations in Poland or can I just build a fence and keep anything there? (within legal boundaries of course, nothing illegal)
The Poles love fences and put them all round their plots - open lawn plots are virtually unheard of here. In my street I cannot think of one house like that.
but there are restrictions about what kind of stuff you can do in your yard (I know you cannot just cut down trees for instance), as to what you can keep there - ask a lawyer if its anything controversial and you plan to spend a lot of money on it. If its just some small issue do it the Polish way - try and wait for someone to tell you to stop.