[TowerTalk] Best way of getting a line over a tree

[Eric]

All this is great input to my question.  I am very intrigued by the 
tennis ball shooter using compressed air or CO2.   I also understand 
there are some commercial units that can be purchased but buying one 
would take all the fun out of actually building one.   What is the best 
tennis ball shooter design out there ?  I like this solution better than 
the sling shot and bow and arrow primarily due to any liability.   If I 
misfired or missed, I think a tennis ball would do less damage than the 
sling shot and bow and arrow. 
Everyone's input has been great, I am really glad that I am part of this 
hobby and there are so many out there that are very willing to help.

Thank you,

Eric