I have recently purchased a decoration item for my tank the only problem is it has to big holes in it that i am afraid my fish will swim into and not be able to get out of. Is there anything that i can use to plug up the holes

I have had fish get stuck in various ornaments. In some cases, I had to use a hammer to break the ornaments. In a few cases, the fish died. You can buy some epoxy sold mostly for reef aquariums but also ponds. It can be molded like clay even while under water and used to plug holes in ornaments. You could also try using rocks, nylon filter material, etc. but those things might not stay in there. Some ornaments I just took out and never used after they caused problems. Fish like to get stuck it seems!

Here is a link to the epoxy at one store:
http://www.drsfostersmith.com/product/prod...&pc=1&N=0&Nty=1