If marching, shouting and demanding don't work, then it's time for the violent approach.
In this clip we see Bulgarian border staff under attack by hordes of illegal Muslim migrants raining rocks and stones down on them.
As they hurl potentially lethal stones at the Bulgarian staff, they dare the staff to return fire. (1:02)
At 2:54 you can see a Bulgarian border guard throwing one of their rocks back at them.
The migrants also appear to be setting fires, occasionally trying to hurl what look like smouldering logs towards the border guards.
At 3:27 armed guards force a retreat by the illegals. But as soon as the Bulgarians move back behind their lines, the offensive begins anew with a fresh round of rocks using other migrants who are clear leaders.
By 4:19 large fires are burning, set by the migrants, perhaps to demarcate territory.
At 6:18 you can see one of the illegal stone throwers holding up a piece of paper with the word, "Serbia" scrawled on it.
The intention of this action seems to have been to get the Bulgarians to allow the horde of migrants to cross into Serbian territory, presumably for a repeat performance at one of the Western borders, most likely Bosnia as they make their way towards Germany.