With each contact your perceive the experience a pleasant, unpleasant or neutral feeling arises which you also perceive as either favorable, unfavorable and neutral. Guarding the sense door is you are aware of the sensation that arose and the perception that arose. Ideally you should be equanimous towards this experience, i.e., not attached or averse to the sensation and stimuli and also realise the evaluation you have given and feed the perception. If not (i.e. you react with craving, aversion or ignorance) fabrications form. In which case you have be be aware of the fabrications also. These manifest as physical feeling in the body having the characteristics of the 6 elements and the metal component has the content 50 cetasikas (52 - 2 = 50 as feeling and perceptions are also cetasikas). See section on The Cetasikas in The Abhidhamma in Practice by N.K.G. Mendis
Also note the initial experience even if you are have a bodily aspect which you have the characteristics of the elements. The sensation is 3 folds are present unpleasant or neutral, etc. For more details on this see Satipatthana related Suttas and literature.
The framework to guard your senses is outlined in the Cha Chakka Sutta through there are more comprehensive dispositions also in other Suttas.
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Latent tendencies LATENT TENDENCIES ARISING THROUGH THE EYE. Bhikshus, dependent on eye and forms, eye-consciousness arises.
When the three meet, there is contact. Dependent on contact, there is what is felt as pleasant, or as painful, or as neither pleasant nor painful.
When one is touched by a pleasant feeling, one delights in it, welcomes it, remains attached to it. Thus one’s latent tendency of lust (rāgânusaya) lies latent.
When one is touched by a painful feeling, one sorrows, grieves, laments, beats one’s breast and falls into confusion. Thus one’s latent tendency of aversion (paṭighânusaya) lies latent.
When one is touched by a feeling that is neither pleasant nor painful, one does not understand it as it really is, the arising, the passing away, the gratification, the danger, and the escape with regards to that feeling. Thus one’s latent tendency of ignorance (avijjā’nusaya) lies latent.
Bhikshus, that one could make an end of suffering here and now, without abandoning lust for pleasurable feelings, without removing aversion towards painful feelings, without uprooting ignorance towards feelings that are neither pleasant nor painful this is impossible.
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Abandoning the latent tendencies ABANDONING LATENT TENDENCIES ARISING THROUGH THE EYE.
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Bhikshus, that one could make an end of suffering here and now, having abandoned lust for pleasurable feelings, having removed aversion towards painful feelings, having uprooted ignorance towards feelings that are neither pleasant nor painful this is possible.
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