Meaning of the hadith “War is deception”

Q: Abu Hurairah and Jabir (may Allah be pleased with them) reported that the Prophet (ﷺ) said, “War is deception.” [Al-Bukhari and Muslim] 

Is it permissible to deliberately spread a false rumour accusing the wife of a prominent political enemy of the Muslims of adultery, with the intention of discrediting him, causing turmoil and distress in his personal life, and thereby hoping to gain a strategic advantage for the Muslims?

Calculating the value of gold for previous years' unpaid zakaat

Q: I wanted to ask some things related to the payment of zakaat. They are as follows: 

I was unaware that I had enough gold previously and now I have to pay zakaat for the last 2.5 years. So will the zakaat of each year be calculated according to the gold value in that year, or according to the current year's gold value? 

If I won't pay it all at once, and do it in installments will I be sinful in delaying it further?

Using a Knobkerrie as a walking stick

Q: I have a friend who walks with a stick. He told me it is sunnah to use a stick. The stick he uses is a knobkerrie. 

Learning this I also bought the same stick, because I liked how it looked. I bought it from a traditional Zulu store as that is the most common place to find that type of stick. 

Recently I was concerned if the stick had any religious connotations within the Zulu kingdom. I researched it on Google and found that it symbolises leadership amongst Zulu clans etc and is also a symbol of manhood and was used as a weapon in old ages. 

Is it okay to continue using the stick for walking or does it count as imitating another nation?