Adam Clarke on Psalms 141:3

Set a watch, O Lord, before my mouth - While there are so many spies on my actions and words, I have need to be doubly guarded, that my enemies may have no advantage against me. Some think the prayer is against impatience; but if he were now going to Gath, it is more natural to suppose that he was praying to be preserved from dishonoring the truth, and from making sinful concessions in a heathen land; and at a court where, from his circumstances, it was natural to suppose he might be tempted to apostasy by the heathen party. The following verse seems to support this opinion.