WOW, the countdown is on, I can't believe in 8 weeks my bubba will be turning one............... anyway my idea is to have a princess castle cake sitting above a moat of jelly with alligators or sharks in the moat. My question is, can I bake a chocolate cake and carve out the top of the cake to resemble a dam then ice that with something (I was thinking RI or BC) then when the jelly has cooled right down fill the 'dam' with the jelly? I just don't know if the jelly will break down the icing or if the icing will hold long enough for the jelly to set and then it wont seep into the cake anyway. Thankyou.

buttercream will hold back your filling. you might want to use piping gel. it comes colorless and you add the color to suit. it's pretty, shiny and translucent. 

what kind of jelly--do you mean something made with gelatine--in the states we call it jello--or do you mean fruit spread--like blueberry jam or something?

you can make 'water' out of piping gel too--

Will have to look into piping gel - I was planning on using a fair bit of jelly as I will use it as a dessert for the kids. Yep Gelatine jelly.

http://veenaartofcakes.blogspot.com/2012/07/how-to-make-piping-gel.html

and you can buy it already made too--

i've never used gelatine jelly on a cake like that--

Thanks Ella and Kate - will have a go at that piping gel recipe as it looks like it would be a good one to have on hand even if I don't use it for this cake. Will have a trial run I think with a few little muffins I think to see what works best and what I like the look of the most.