English does not use "it's a real safe bet" or "you cannot go wrong with this." to describe an activity. It is used to describe an object or a choice of some sort that will deliver an objective or goal.
A: "I hear that you need a new laptop - IBMs are a safe bet / You can't go wrong with an IBM."
So, there has to be a goal/aim/required result - it would have to be: A:"So you want to loose weight? Swimming is a safe bet."
Can you give us a full sentence that will show how you want to use the phrase?
"So it’s really the perfect day out if you want to make sure everybody in your group has a good time. It’s near impossible to be disappointed."is better because if something is a safe bet, it is usually not the "exciting" option.