I created a multivariate linear model and am wondering how I can validate the model? The samples are environmental samples and due to a few limitations I am not able to validate by collecting more samples and testing the model. So I am trying to find the best way to validate the model using either a split-half analysis or some form of cross validation? Any help would be greatly appreciated.

Model was made on SAS ODA but I can use R or any platform necessary to validate it. I have original data and observed versus predicated data.