The Shulchan Aruch/Mishna Berurah 102 (4)  writes that one may not walk within four Amos in front of somebody praying the Amidah.
What constitutes an acceptable barrier in front of the person so that another person can pass by?
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The Chaye Adam (26:4) brings 2 separate answers:
The CA gives stronger support to the 2nd answer, though I have seen others pasken like the 1st.
The 2nd answer does not seem to be limited to the CA's alternate reason for the restriction- that the passer-by separates the davener from the shechina (26:3). Rather, even according to the generally known reason- that passing by distracts the daveners attention, the CA holds that the rabbinic restriction is limited to the domain of the davener. If his attention will be distracted from beyond the domain, too bad. Therefore a 4x10 partition in front of the davener would work as well.