Well....I was not referring to attacks by other religious leaders on Guru Nanak. I was referring to "physical" attacks which were common those days (even today). There were no highways or patrols those days. It is a well known fact that all travelers (traders, etc) used to either carry some weapon or hired someone to protect themselves and their property.
When we undertake a small day trip to any city nearby, we pack everything that we might need for the trip, including clothes, food, drinks, cash and we protect our property by properly locking our cars, home, etc. Guru Nanak embarked on multi year journeys and wouldn't he had thought of logistics of undertaking those journeys?
The financial aspect for undertaking multi year journeys is also very significant. We all know Guru Nanak was born in a wealthy family and would have had no issues in arranging for funds for his journeys. But is it practical to carry wads of cash (or bags of coins) needed for multi-year trips? How did Guru Nanak arrange money to fund his travels? Wherever Guru Nanak visited, local people would have definitely offered him some gifts/funds which needed protection too. I am sure he must have distributed most of the funds to the needy, but he definitely saved some portion for his travels. Didn't that money need some physical protection?
It is very immature to assume that Guru Nanak undertook all those journeys without properly thinking about the "risks" involved in his travels. As a great visionary, I am sure he must have thought about those "risks" (of getting physically attacked by robbers and thieves) and surely would have taken steps to mitigate those risks (by carrying some sort of weapon - usually kirpan or a dagger).